diff --git a/includes/Category.php b/includes/Category.php
index 1ebd605c355..d558dbc44db 100644
--- a/includes/Category.php
+++ b/includes/Category.php
@@ -168,7 +168,7 @@ class Category {
 	 * @param Title $title Optional title object for the category represented by
 	 *   the given row. May be provided if it is already known, to avoid having
 	 *   to re-create a title object later.
-	 * @return Category
+	 * @return Category|false
 	 */
 	public static function newFromRow( $row, $title = null ) {
 		$cat = new self();
diff --git a/includes/EditPage.php b/includes/EditPage.php
index f37ce34c4a3..7a0a11f7d17 100644
--- a/includes/EditPage.php
+++ b/includes/EditPage.php
@@ -295,7 +295,7 @@ class EditPage {
 	/** @var bool Has a summary been preset using GET parameter &summary= ? */
 	public $hasPresetSummary = false;
 
-	/** @var bool */
+	/** @var Revision|bool */
 	public $mBaseRevision = false;
 
 	/** @var bool */
diff --git a/includes/GitInfo.php b/includes/GitInfo.php
index de7e8c28e2d..4351acc0e9b 100644
--- a/includes/GitInfo.php
+++ b/includes/GitInfo.php
@@ -46,7 +46,7 @@ class GitInfo {
 	protected $cache = [];
 
 	/**
-	 * Map of repo URLs to viewer URLs. Access via static method getViewers().
+	 * @var array|false Map of repo URLs to viewer URLs. Access via static method getViewers().
 	 */
 	private static $viewers = false;
 
diff --git a/includes/GlobalFunctions.php b/includes/GlobalFunctions.php
index b3ccc5675ab..4d27f68005a 100644
--- a/includes/GlobalFunctions.php
+++ b/includes/GlobalFunctions.php
@@ -545,7 +545,7 @@ function wfAppendQuery( $url, $query ) {
  * @param string $url Either fully-qualified or a local path + query
  * @param string $defaultProto One of the PROTO_* constants. Determines the
  *    protocol to use if $url or $wgServer is protocol-relative
- * @return string Fully-qualified URL, current-path-relative URL or false if
+ * @return string|false Fully-qualified URL, current-path-relative URL or false if
  *    no valid URL can be constructed
  */
 function wfExpandUrl( $url, $defaultProto = PROTO_CURRENT ) {
diff --git a/includes/HistoryBlob.php b/includes/HistoryBlob.php
index b17a2f5e2ad..3d86201c946 100644
--- a/includes/HistoryBlob.php
+++ b/includes/HistoryBlob.php
@@ -239,7 +239,7 @@ class HistoryBlobStub {
 	}
 
 	/**
-	 * @return string
+	 * @return string|false
 	 */
 	function getText() {
 		if ( isset( self::$blobCache[$this->mOldId] ) ) {
diff --git a/includes/OutputPage.php b/includes/OutputPage.php
index bae871e445d..1d536bbeea6 100644
--- a/includes/OutputPage.php
+++ b/includes/OutputPage.php
@@ -2176,7 +2176,7 @@ class OutputPage extends ContextSource {
 	 * if there isn't one. This is used by Skin to determine whether to enable
 	 * JavaScript frame-breaking, for clients that don't support X-Frame-Options.
 	 *
-	 * @return string
+	 * @return string|false
 	 */
 	public function getFrameOptions() {
 		$config = $this->getConfig();
diff --git a/includes/PathRouter.php b/includes/PathRouter.php
index 049b32f64e3..cc6fc4a399a 100644
--- a/includes/PathRouter.php
+++ b/includes/PathRouter.php
@@ -364,7 +364,7 @@ class PathRouterPatternReplacer {
 	 * difference between a $1 that was not replaced and a $1 that was part of
 	 * the content a $1 was replaced with.
 	 * @param string $value
-	 * @return string
+	 * @return string|false
 	 */
 	public function replace( $value ) {
 		$this->error = false;
diff --git a/includes/ProtectionForm.php b/includes/ProtectionForm.php
index 451635e319d..454ffcc978d 100644
--- a/includes/ProtectionForm.php
+++ b/includes/ProtectionForm.php
@@ -148,7 +148,7 @@ class ProtectionForm {
 	 *
 	 * @param string $action
 	 *
-	 * @return string 14-char timestamp or "infinity", or false if the input was invalid
+	 * @return string|false 14-char timestamp or "infinity", or false if the input was invalid
 	 */
 	function getExpiry( $action ) {
 		if ( $this->mExpirySelection[$action] == 'existing' ) {
diff --git a/includes/Revision.php b/includes/Revision.php
index b812191398a..a74501f5ef0 100644
--- a/includes/Revision.php
+++ b/includes/Revision.php
@@ -874,7 +874,7 @@ class Revision implements IDBAccessObject {
 	/**
 	 * Fetch revision's user id without regard for the current user's permissions
 	 *
-	 * @return string
+	 * @return int
 	 * @deprecated since 1.25, use getUser( Revision::RAW )
 	 */
 	public function getRawUser() {
@@ -1269,7 +1269,7 @@ class Revision implements IDBAccessObject {
 	 *   (same as the the wiki $row was loaded from) or false to indicate the local
 	 *   wiki (this is the default). Otherwise, it must be a symbolic wiki database
 	 *   identifier as understood by the LoadBalancer class.
-	 * @return string Text the text requested or false on failure
+	 * @return string|false Text the text requested or false on failure
 	 */
 	public static function getRevisionText( $row, $prefix = 'old_', $wiki = false ) {
 
diff --git a/includes/SiteConfiguration.php b/includes/SiteConfiguration.php
index 885f926fa27..8d9256b8114 100644
--- a/includes/SiteConfiguration.php
+++ b/includes/SiteConfiguration.php
@@ -274,7 +274,7 @@ class SiteConfiguration {
 	 * @param string $from
 	 * @param string $to
 	 * @param string|array $in
-	 * @return string
+	 * @return string|array
 	 */
 	function doReplace( $from, $to, $in ) {
 		if ( is_string( $in ) ) {
diff --git a/includes/Title.php b/includes/Title.php
index 3c51baebe2c..1507a0da666 100644
--- a/includes/Title.php
+++ b/includes/Title.php
@@ -835,7 +835,7 @@ class Title implements LinkTarget {
 	/**
 	 * Returns the DB name of the distant wiki which owns the object.
 	 *
-	 * @return string The DB name
+	 * @return string|false The DB name
 	 */
 	public function getTransWikiID() {
 		if ( !$this->isExternal() ) {
@@ -974,7 +974,7 @@ class Title implements LinkTarget {
 	/**
 	 * Get the namespace text
 	 *
-	 * @return string Namespace text
+	 * @return string|false Namespace text
 	 */
 	public function getNsText() {
 		if ( $this->isExternal() ) {
@@ -4436,7 +4436,7 @@ class Title implements LinkTarget {
 	 * Get the last touched timestamp
 	 *
 	 * @param IDatabase $db Optional db
-	 * @return string Last-touched timestamp
+	 * @return string|false Last-touched timestamp
 	 */
 	public function getTouched( $db = null ) {
 		if ( $db === null ) {
diff --git a/includes/WebRequest.php b/includes/WebRequest.php
index 3ef3bc1e0be..ecc5caaba03 100644
--- a/includes/WebRequest.php
+++ b/includes/WebRequest.php
@@ -238,7 +238,7 @@ class WebRequest {
 	 * This is for use prior to Setup.php, when no WebRequest object is available.
 	 * At other times, use the non-static function getProtocol().
 	 *
-	 * @return array
+	 * @return string
 	 */
 	public static function detectProtocol() {
 		if ( ( !empty( $_SERVER['HTTPS'] ) && $_SERVER['HTTPS'] !== 'off' ) ||
diff --git a/includes/WikiMap.php b/includes/WikiMap.php
index 37f85ea27c1..f7b8d2f16df 100644
--- a/includes/WikiMap.php
+++ b/includes/WikiMap.php
@@ -141,7 +141,7 @@ class WikiMap {
 	 * @param string $wikiID Wiki'd id (generally database name)
 	 * @param string $page Page name (must be normalised before calling this function!)
 	 * @param string $text Link's text; optional, default to $page
-	 * @return string HTML link or false if the wiki was not found
+	 * @return string|false HTML link or false if the wiki was not found
 	 */
 	public static function makeForeignLink( $wikiID, $page, $text = null ) {
 		if ( !$text ) {
diff --git a/includes/api/ApiBase.php b/includes/api/ApiBase.php
index a40593f6bd5..68acb5259ba 100644
--- a/includes/api/ApiBase.php
+++ b/includes/api/ApiBase.php
@@ -2229,7 +2229,7 @@ abstract class ApiBase extends ContextSource {
 	 * "apihelp-{$this->getModulePath()}-description".
 	 *
 	 * @deprecated since 1.25
-	 * @return Message|string|array
+	 * @return Message|string|array|false
 	 */
 	protected function getDescription() {
 		return false;
diff --git a/includes/api/ApiParamInfo.php b/includes/api/ApiParamInfo.php
index a9b3dde9472..46ba34b4404 100644
--- a/includes/api/ApiParamInfo.php
+++ b/includes/api/ApiParamInfo.php
@@ -237,7 +237,7 @@ class ApiParamInfo extends ApiBase {
 
 	/**
 	 * @param ApiBase $module
-	 * @return ApiResult
+	 * @return array
 	 */
 	private function getModuleInfo( $module ) {
 		$ret = [];
diff --git a/includes/api/ApiQueryBase.php b/includes/api/ApiQueryBase.php
index af2aed55047..281fb61eb72 100644
--- a/includes/api/ApiQueryBase.php
+++ b/includes/api/ApiQueryBase.php
@@ -584,7 +584,7 @@ abstract class ApiQueryBase extends ApiBase {
 	 * @return bool
 	 */
 	public function validateSha1Hash( $hash ) {
-		return preg_match( '/^[a-f0-9]{40}$/', $hash );
+		return (bool)preg_match( '/^[a-f0-9]{40}$/', $hash );
 	}
 
 	/**
@@ -592,7 +592,7 @@ abstract class ApiQueryBase extends ApiBase {
 	 * @return bool
 	 */
 	public function validateSha1Base36Hash( $hash ) {
-		return preg_match( '/^[a-z0-9]{31}$/', $hash );
+		return (bool)preg_match( '/^[a-z0-9]{31}$/', $hash );
 	}
 
 	/**
diff --git a/includes/api/ApiQueryCategoryMembers.php b/includes/api/ApiQueryCategoryMembers.php
index 02961aa299d..3a8847c3396 100644
--- a/includes/api/ApiQueryCategoryMembers.php
+++ b/includes/api/ApiQueryCategoryMembers.php
@@ -53,7 +53,7 @@ class ApiQueryCategoryMembers extends ApiQueryGeneratorBase {
 	 */
 	private function validateHexSortkey( $hexSortkey ) {
 		// A hex sortkey has an unbound number of 2 letter pairs
-		return preg_match( '/^(?:[a-fA-F0-9]{2})*$/D', $hexSortkey );
+		return (bool)preg_match( '/^(?:[a-fA-F0-9]{2})*$/D', $hexSortkey );
 	}
 
 	/**
diff --git a/includes/api/ApiStashEdit.php b/includes/api/ApiStashEdit.php
index e29fda536f6..37ee3e76232 100644
--- a/includes/api/ApiStashEdit.php
+++ b/includes/api/ApiStashEdit.php
@@ -168,7 +168,7 @@ class ApiStashEdit extends ApiBase {
 	 * @param Content $content Edit content
 	 * @param User $user
 	 * @param string $summary Edit summary
-	 * @return integer ApiStashEdit::ERROR_* constant
+	 * @return string ApiStashEdit::ERROR_* constant
 	 * @since 1.25
 	 */
 	public static function parseAndStash( WikiPage $page, Content $content, User $user, $summary ) {
diff --git a/includes/cache/FileCacheBase.php b/includes/cache/FileCacheBase.php
index e25f882b378..6d5f8c3e55a 100644
--- a/includes/cache/FileCacheBase.php
+++ b/includes/cache/FileCacheBase.php
@@ -154,7 +154,7 @@ abstract class FileCacheBase {
 	/**
 	 * Save and compress text to the cache
 	 * @param string $text
-	 * @return string Compressed text
+	 * @return string|false Compressed text
 	 */
 	public function saveText( $text ) {
 		if ( $this->useGzip() ) {
diff --git a/includes/cache/localisation/LocalisationCache.php b/includes/cache/localisation/LocalisationCache.php
index 4b6362fb0be..90b3de1ac1b 100644
--- a/includes/cache/localisation/LocalisationCache.php
+++ b/includes/cache/localisation/LocalisationCache.php
@@ -313,7 +313,7 @@ class LocalisationCache {
 	 * array.
 	 * @param string $code
 	 * @param string $key
-	 * @return bool|null|string
+	 * @return bool|null|string|string[]
 	 */
 	public function getSubitemList( $code, $key ) {
 		if ( in_array( $key, self::$splitKeys ) ) {
diff --git a/includes/db/DatabaseMssql.php b/includes/db/DatabaseMssql.php
index 2f9f8093232..7c4bb3b7215 100644
--- a/includes/db/DatabaseMssql.php
+++ b/includes/db/DatabaseMssql.php
@@ -332,7 +332,7 @@ class DatabaseMssql extends Database {
 	}
 
 	/**
-	 * @return string
+	 * @return string|int
 	 */
 	public function lastErrno() {
 		$err = sqlsrv_errors( SQLSRV_ERR_ALL );
diff --git a/includes/db/DatabaseOracle.php b/includes/db/DatabaseOracle.php
index 925850653f0..c3502f60adb 100644
--- a/includes/db/DatabaseOracle.php
+++ b/includes/db/DatabaseOracle.php
@@ -993,7 +993,7 @@ class DatabaseOracle extends Database {
 	 *
 	 * @param array|string $table
 	 * @param string $field
-	 * @return ORAField|ORAResult
+	 * @return ORAField|ORAResult|false
 	 */
 	private function fieldInfoMulti( $table, $field ) {
 		$field = strtoupper( $field );
diff --git a/includes/debug/logger/LegacyLogger.php b/includes/debug/logger/LegacyLogger.php
index 4614c46b6d2..baf4637e835 100644
--- a/includes/debug/logger/LegacyLogger.php
+++ b/includes/debug/logger/LegacyLogger.php
@@ -378,7 +378,7 @@ class LegacyLogger extends AbstractLogger {
 			if ( is_nan( $item ) ) {
 				return 'NaN';
 			}
-			return $item;
+			return (string)$item;
 		}
 
 		if ( is_scalar( $item ) ) {
diff --git a/includes/diff/DairikiDiff.php b/includes/diff/DairikiDiff.php
index d38319e1ac9..a08bd9ed9b0 100644
--- a/includes/diff/DairikiDiff.php
+++ b/includes/diff/DairikiDiff.php
@@ -67,7 +67,7 @@ abstract class DiffOp {
 
 	/**
 	 * @param int $i
-	 * @return string|null
+	 * @return string[]|string|null
 	 */
 	public function getClosing( $i = null ) {
 		if ( $i === null ) {
diff --git a/includes/diff/DifferenceEngine.php b/includes/diff/DifferenceEngine.php
index bd65fb42dc8..ca8a48cedf9 100644
--- a/includes/diff/DifferenceEngine.php
+++ b/includes/diff/DifferenceEngine.php
@@ -210,7 +210,7 @@ class DifferenceEngine extends ContextSource {
 		if ( $link ) {
 			return "[$link $id]";
 		} else {
-			return $id;
+			return (string)$id;
 		}
 	}
 
diff --git a/includes/filerepo/FileRepo.php b/includes/filerepo/FileRepo.php
index 66dab992172..41f52815d25 100644
--- a/includes/filerepo/FileRepo.php
+++ b/includes/filerepo/FileRepo.php
@@ -99,7 +99,7 @@ class FileRepo {
 	 */
 	protected $pathDisclosureProtection = 'simple';
 
-	/** @var bool Public zone URL. */
+	/** @var string|false Public zone URL. */
 	protected $url;
 
 	/** @var string The base thumbnail URL. Defaults to "<url>/thumb". */
@@ -309,7 +309,7 @@ class FileRepo {
 	 * @return bool Whether non-ASCII path characters are allowed
 	 */
 	public function backendSupportsUnicodePaths() {
-		return ( $this->getBackend()->getFeatures() & FileBackend::ATTR_UNICODE_PATHS );
+		return (bool)( $this->getBackend()->getFeatures() & FileBackend::ATTR_UNICODE_PATHS );
 	}
 
 	/**
@@ -737,7 +737,7 @@ class FileRepo {
 	 * constructor, whereas local repositories use the local Title functions.
 	 *
 	 * @param string $name
-	 * @return string
+	 * @return string|false
 	 */
 	public function getDescriptionUrl( $name ) {
 		$encName = wfUrlencode( $name );
@@ -771,7 +771,7 @@ class FileRepo {
 	 *
 	 * @param string $name Name of image to fetch
 	 * @param string $lang Language to fetch it in, if any.
-	 * @return string
+	 * @return string|false
 	 */
 	public function getDescriptionRenderUrl( $name, $lang = null ) {
 		$query = 'action=render';
diff --git a/includes/filerepo/ForeignAPIRepo.php b/includes/filerepo/ForeignAPIRepo.php
index 4176c8240ee..ca417187e0c 100644
--- a/includes/filerepo/ForeignAPIRepo.php
+++ b/includes/filerepo/ForeignAPIRepo.php
@@ -109,7 +109,7 @@ class ForeignAPIRepo extends FileRepo {
 	 *
 	 * @param Title $title
 	 * @param string|bool $time
-	 * @return File
+	 * @return File|false
 	 */
 	function newFile( $title, $time = false ) {
 		if ( $time ) {
diff --git a/includes/filerepo/RepoGroup.php b/includes/filerepo/RepoGroup.php
index d47624f8cde..2edd6d09142 100644
--- a/includes/filerepo/RepoGroup.php
+++ b/includes/filerepo/RepoGroup.php
@@ -334,7 +334,7 @@ class RepoGroup {
 	/**
 	 * Get the repo instance by its name
 	 * @param string $name
-	 * @return bool
+	 * @return FileRepo|bool
 	 */
 	function getRepoByName( $name ) {
 		if ( !$this->reposInitialised ) {
diff --git a/includes/filerepo/file/ArchivedFile.php b/includes/filerepo/file/ArchivedFile.php
index 921e129c36f..9a7a55be9eb 100644
--- a/includes/filerepo/file/ArchivedFile.php
+++ b/includes/filerepo/file/ArchivedFile.php
@@ -81,7 +81,7 @@ class ArchivedFile {
 	/** @var string SHA-1 hash of file content */
 	private $sha1;
 
-	/** @var string Number of pages of a multipage document, or false for
+	/** @var int|false Number of pages of a multipage document, or false for
 	 * documents which aren't multipage documents
 	 */
 	private $pageCount;
@@ -496,7 +496,7 @@ class ArchivedFile {
 	 * Return the user name of the uploader.
 	 *
 	 * @deprecated since 1.23 Use getUser( 'text' ) instead.
-	 * @return string
+	 * @return string|int
 	 */
 	public function getUserText() {
 		wfDeprecated( __METHOD__, '1.23' );
@@ -511,7 +511,7 @@ class ArchivedFile {
 	/**
 	 * Return upload description.
 	 *
-	 * @return string
+	 * @return string|int
 	 */
 	public function getDescription() {
 		$this->load();
diff --git a/includes/filerepo/file/File.php b/includes/filerepo/file/File.php
index 9188cd91405..8be662f1f46 100644
--- a/includes/filerepo/file/File.php
+++ b/includes/filerepo/file/File.php
@@ -127,7 +127,7 @@ abstract class File implements IDBAccessObject {
 	/** @var string Relative path including trailing slash */
 	protected $hashPath;
 
-	/** @var string Number of pages of a multipage document, or false for
+	/** @var string|false Number of pages of a multipage document, or false for
 	 *    documents which aren't multipage documents
 	 */
 	protected $pageCount;
@@ -535,7 +535,7 @@ abstract class File implements IDBAccessObject {
 	/**
 	 * Get the duration of a media file in seconds
 	 *
-	 * @return int
+	 * @return float|int
 	 */
 	public function getLength() {
 		$handler = $this->getHandler();
@@ -909,7 +909,7 @@ abstract class File implements IDBAccessObject {
 	 *
 	 * @param array $handlerParams
 	 *
-	 * @return string
+	 * @return ThumbnailImage|MediaTransformOutput|bool False on failure
 	 */
 	function getUnscaledThumb( $handlerParams = [] ) {
 		$hp =& $handlerParams;
@@ -1963,7 +1963,7 @@ abstract class File implements IDBAccessObject {
 	 * Returns the number of pages of a multipage document, or false for
 	 * documents which aren't multipage documents
 	 *
-	 * @return bool|int
+	 * @return string|bool|int
 	 */
 	function pageCount() {
 		if ( !isset( $this->pageCount ) ) {
@@ -1991,7 +1991,7 @@ abstract class File implements IDBAccessObject {
 		if ( $srcWidth == 0 ) {
 			return 0;
 		} else {
-			return round( $srcHeight * $dstWidth / $srcWidth );
+			return (int)round( $srcHeight * $dstWidth / $srcWidth );
 		}
 	}
 
@@ -2003,7 +2003,7 @@ abstract class File implements IDBAccessObject {
 	 *  a good reason. This method skips all caches.
 	 *
 	 * @param string $filePath The path to the file (e.g. From getLocalPathRef() )
-	 * @return array The width, followed by height, with optionally more things after
+	 * @return array|false The width, followed by height, with optionally more things after
 	 */
 	function getImageSize( $filePath ) {
 		if ( !$this->getHandler() ) {
@@ -2031,7 +2031,7 @@ abstract class File implements IDBAccessObject {
 	 * Get the HTML text of the description page, if available
 	 *
 	 * @param bool|Language $lang Optional language to fetch description in
-	 * @return string
+	 * @return string|false
 	 */
 	function getDescriptionText( $lang = false ) {
 		global $wgLang;
@@ -2122,7 +2122,7 @@ abstract class File implements IDBAccessObject {
 	/**
 	 * Get the deletion archive key, "<sha1>.<ext>"
 	 *
-	 * @return string
+	 * @return string|false
 	 */
 	function getStorageKey() {
 		$hash = $this->getSha1();
diff --git a/includes/filerepo/file/ForeignDBFile.php b/includes/filerepo/file/ForeignDBFile.php
index df50a670a23..c6c49b4ca49 100644
--- a/includes/filerepo/file/ForeignDBFile.php
+++ b/includes/filerepo/file/ForeignDBFile.php
@@ -121,7 +121,7 @@ class ForeignDBFile extends LocalFile {
 
 	/**
 	 * @param bool|Language $lang Optional language to fetch description in.
-	 * @return string
+	 * @return string|false
 	 */
 	function getDescriptionText( $lang = false ) {
 		global $wgLang;
diff --git a/includes/htmlform/HTMLFormField.php b/includes/htmlform/HTMLFormField.php
index 71aa2754498..804bbff451c 100644
--- a/includes/htmlform/HTMLFormField.php
+++ b/includes/htmlform/HTMLFormField.php
@@ -1034,7 +1034,7 @@ abstract class HTMLFormField {
 	 * with integer 0 as a value.
 	 *
 	 * @param array $array
-	 * @return array
+	 * @return array|string
 	 */
 	public static function forceToStringRecursive( $array ) {
 		if ( is_array( $array ) ) {
diff --git a/includes/htmlform/fields/HTMLButtonField.php b/includes/htmlform/fields/HTMLButtonField.php
index 285490bc986..500b5020c82 100644
--- a/includes/htmlform/fields/HTMLButtonField.php
+++ b/includes/htmlform/fields/HTMLButtonField.php
@@ -127,6 +127,6 @@ class HTMLButtonField extends HTMLFormField {
 		$request = $this->mParent
 			? $this->mParent->getRequest()
 			: RequestContext::getMain()->getRequest();
-		return preg_match( '/MSIE [1-7]\./i', $request->getHeader( 'User-Agent' ) );
+		return (bool)preg_match( '/MSIE [1-7]\./i', $request->getHeader( 'User-Agent' ) );
 	}
 }
diff --git a/includes/htmlform/fields/HTMLMultiSelectField.php b/includes/htmlform/fields/HTMLMultiSelectField.php
index 05a2ba6d5e9..23044bd6ff2 100644
--- a/includes/htmlform/fields/HTMLMultiSelectField.php
+++ b/includes/htmlform/fields/HTMLMultiSelectField.php
@@ -149,7 +149,7 @@ class HTMLMultiSelectField extends HTMLFormField implements HTMLNestedFilterable
 	/**
 	 * @param WebRequest $request
 	 *
-	 * @return string
+	 * @return string|array
 	 */
 	public function loadDataFromRequest( $request ) {
 		if ( $this->isSubmitAttempt( $request ) ) {
diff --git a/includes/htmlform/fields/HTMLSizeFilterField.php b/includes/htmlform/fields/HTMLSizeFilterField.php
index d94eb8dff37..5ad7ee3414d 100644
--- a/includes/htmlform/fields/HTMLSizeFilterField.php
+++ b/includes/htmlform/fields/HTMLSizeFilterField.php
@@ -49,7 +49,7 @@ class HTMLSizeFilterField extends HTMLIntField {
 	/**
 	 * @param WebRequest $request
 	 *
-	 * @return string
+	 * @return string|int
 	 */
 	public function loadDataFromRequest( $request ) {
 		$size = $request->getInt( $this->mName );
diff --git a/includes/http/Http.php b/includes/http/Http.php
index 8255bb344ed..779d6063467 100644
--- a/includes/http/Http.php
+++ b/includes/http/Http.php
@@ -142,7 +142,7 @@ class Http {
 	 * @return bool
 	 */
 	public static function isValidURI( $uri ) {
-		return preg_match(
+		return (bool)preg_match(
 			'/^https?:\/\/[^\/\s]\S*$/D',
 			$uri
 		);
diff --git a/includes/installer/Installer.php b/includes/installer/Installer.php
index 03f997471b4..9dc80326347 100644
--- a/includes/installer/Installer.php
+++ b/includes/installer/Installer.php
@@ -567,7 +567,7 @@ abstract class Installer {
 	/**
 	 * Determine if LocalSettings.php exists. If it does, return its variables.
 	 *
-	 * @return array
+	 * @return array|false
 	 */
 	public static function getExistingLocalSettings() {
 		global $IP;
@@ -1080,7 +1080,7 @@ abstract class Installer {
 	/**
 	 * Convert a hex string representing a Unicode code point to that code point.
 	 * @param string $c
-	 * @return string
+	 * @return string|false
 	 */
 	protected function unicodeChar( $c ) {
 		$c = hexdec( $c );
diff --git a/includes/installer/LocalSettingsGenerator.php b/includes/installer/LocalSettingsGenerator.php
index a9e3e8584b9..697188ef081 100644
--- a/includes/installer/LocalSettingsGenerator.php
+++ b/includes/installer/LocalSettingsGenerator.php
@@ -109,7 +109,7 @@ class LocalSettingsGenerator {
 	 *
 	 * @param string $string
 	 *
-	 * @return string
+	 * @return string|false
 	 */
 	public static function escapePhpString( $string ) {
 		if ( is_array( $string ) || is_object( $string ) ) {
diff --git a/includes/interwiki/ClassicInterwikiLookup.php b/includes/interwiki/ClassicInterwikiLookup.php
index 0e107b3d112..4ccca9785e8 100644
--- a/includes/interwiki/ClassicInterwikiLookup.php
+++ b/includes/interwiki/ClassicInterwikiLookup.php
@@ -187,7 +187,7 @@ class ClassicInterwikiLookup implements InterwikiLookup {
 	 * @note More logic is explained in DefaultSettings.
 	 *
 	 * @param string $prefix Interwiki prefix
-	 * @return Interwiki
+	 * @return Interwiki|false
 	 */
 	private function getInterwikiCached( $prefix ) {
 		$value = $this->getInterwikiCacheEntry( $prefix );
diff --git a/includes/jobqueue/aggregator/JobQueueAggregatorRedis.php b/includes/jobqueue/aggregator/JobQueueAggregatorRedis.php
index 6ae883712e2..d9457c603f1 100644
--- a/includes/jobqueue/aggregator/JobQueueAggregatorRedis.php
+++ b/includes/jobqueue/aggregator/JobQueueAggregatorRedis.php
@@ -126,7 +126,7 @@ class JobQueueAggregatorRedis extends JobQueueAggregator {
 
 	/**
 	 * @param string $name
-	 * @return string
+	 * @return string[]
 	 */
 	private function decodeQueueName( $name ) {
 		list( $type, $wiki ) = explode( '/', $name, 2 );
diff --git a/includes/libs/ExplodeIterator.php b/includes/libs/ExplodeIterator.php
index 3b34d9bce0d..d4abdc86e85 100644
--- a/includes/libs/ExplodeIterator.php
+++ b/includes/libs/ExplodeIterator.php
@@ -40,7 +40,7 @@ class ExplodeIterator implements Iterator {
 	// The position after the end of the next delimiter
 	private $endPos;
 
-	// The current token
+	/** @var string|false The current token */
 	private $current;
 
 	/**
diff --git a/includes/libs/HashRing.php b/includes/libs/HashRing.php
index 70ce31d713d..4ddb8131d52 100644
--- a/includes/libs/HashRing.php
+++ b/includes/libs/HashRing.php
@@ -32,7 +32,7 @@ class HashRing {
 	/** @var Array (location => (start, end)) */
 	protected $ring = [];
 
-	/** @var Array (location => (start, end)) */
+	/** @var HashRing|null */
 	protected $liveRing;
 	/** @var Array (location => UNIX timestamp) */
 	protected $ejectionExpiries = [];
diff --git a/includes/libs/filebackend/FileBackendStore.php b/includes/libs/filebackend/FileBackendStore.php
index bd2ce5ddfb1..a7ceab2ed51 100644
--- a/includes/libs/filebackend/FileBackendStore.php
+++ b/includes/libs/filebackend/FileBackendStore.php
@@ -729,7 +729,7 @@ abstract class FileBackendStore extends FileBackend {
 	/**
 	 * @see FileBackendStore::getFileXAttributes()
 	 * @param array $params
-	 * @return bool|string
+	 * @return array[][]
 	 */
 	protected function doGetFileXAttributes( array $params ) {
 		return [ 'headers' => [], 'metadata' => [] ]; // not supported
diff --git a/includes/libs/filebackend/SwiftFileBackend.php b/includes/libs/filebackend/SwiftFileBackend.php
index 08cb388e2a2..d40e896488c 100644
--- a/includes/libs/filebackend/SwiftFileBackend.php
+++ b/includes/libs/filebackend/SwiftFileBackend.php
@@ -1701,7 +1701,7 @@ class SwiftFileBackend extends FileBackendStore {
 	 * @param array $creds From getAuthentication()
 	 * @param string $container
 	 * @param string $object
-	 * @return array
+	 * @return string
 	 */
 	protected function storageUrl( array $creds, $container = null, $object = null ) {
 		$parts = [ $creds['storage_url'] ];
diff --git a/languages/Language.php b/languages/Language.php
index 2e4ef89c5c5..4cb491a0c15 100644
--- a/languages/Language.php
+++ b/languages/Language.php
@@ -2577,7 +2577,7 @@ class Language {
 
 	/**
 	 * @param string $key
-	 * @return array|null
+	 * @return string|null
 	 */
 	public function getMessage( $key ) {
 		return self::$dataCache->getSubitem( $this->mCode, 'messages', $key );