diff --git a/includes/media/WebPHandler.php b/includes/media/WebPHandler.php
index 1e6e0cbd22a..f0993996df5 100644
--- a/includes/media/WebPHandler.php
+++ b/includes/media/WebPHandler.php
@@ -277,13 +277,13 @@ class WebPHandler extends BitmapHandler {
 			return [];
 		}
 		// Bytes 9-12 contain the image size
-		// Bits 0-13 are width-1; bits 15-27 are height-1
+		// Bits 0-13 are width-1; bits 14-27 are height-1
 		$imageSize = unpack( 'C4', substr( $header, 9, 4 ) );
 		return [
 				'compression' => 'lossless',
 				'width' => ( $imageSize[1] | ( ( $imageSize[2] & 0x3F ) << 8 ) ) + 1,
 				'height' => ( ( ( $imageSize[2] & 0xC0 ) >> 6 ) |
-						( $imageSize[3] << 2 ) | ( ( $imageSize[4] & 0x03 ) << 10 ) ) + 1
+						( $imageSize[3] << 2 ) | ( ( $imageSize[4] & 0x0F ) << 10 ) ) + 1
 		];
 	}
 
diff --git a/tests/phpunit/data/media/webp_ll_large.webp b/tests/phpunit/data/media/webp_ll_large.webp
new file mode 100644
index 00000000000..4fcfa534623
Binary files /dev/null and b/tests/phpunit/data/media/webp_ll_large.webp differ
diff --git a/tests/phpunit/includes/media/WebPHandlerTest.php b/tests/phpunit/includes/media/WebPHandlerTest.php
index a75d8904239..10f5e387167 100644
--- a/tests/phpunit/includes/media/WebPHandlerTest.php
+++ b/tests/phpunit/includes/media/WebPHandlerTest.php
@@ -284,6 +284,22 @@ class WebPHandlerTest extends MediaWikiIntegrationTestCase {
 					]
 				]
 			],
+			// Lossless red square at max resolution to confirm height decoding
+			[
+				__DIR__ . '/../../data/media/webp_ll_large.webp',
+				[
+					'width' => 16383,
+					'height' => 16383,
+					'metadata' => [
+						'compression' => 'lossless',
+						'width' => 16383,
+						'height' => 16383,
+						'metadata' => [
+							'_MW_WEBP_VERSION' => 2,
+						],
+					],
+				]
+			],
 
 			// Error cases
 			[