diff --git a/includes/DefaultSettings.php b/includes/DefaultSettings.php
index 1eefa55d65c..932cf83c96a 100644
--- a/includes/DefaultSettings.php
+++ b/includes/DefaultSettings.php
@@ -4156,11 +4156,10 @@ $wgParserTestRemote = false;
 
 
 /**
- * Overwrite the caching key prefix with custom value.  Do not set if using
- * load balancer, since it depends on the key being in certain format.
+ * Overwrite the caching key prefix with custom value.
  * @since 1.19
  */
-$wgWikiID = false;
+$wgCachePrefix = false;
 
 /**
  * Display the new debugging toolbar. This also enables profiling on database
diff --git a/includes/GlobalFunctions.php b/includes/GlobalFunctions.php
index 02c6c943b91..76248875161 100644
--- a/includes/GlobalFunctions.php
+++ b/includes/GlobalFunctions.php
@@ -3210,8 +3210,10 @@ function wfGetPrecompiledData( $name ) {
  * @return String
  */
 function wfMemcKey( /*... */ ) {
+	global $wgCachePrefix;
+	$prefix = $wgCachePrefix === false ? wfWikiID() : $wgCachePrefix;
 	$args = func_get_args();
-	$key = wfWikiID() . ':' . implode( ':', $args );
+	$key = $prefix . ':' . implode( ':', $args );
 	$key = str_replace( ' ', '_', $key );
 	return $key;
 }
@@ -3241,10 +3243,8 @@ function wfForeignMemcKey( $db, $prefix /*, ... */ ) {
  * @return String
  */
 function wfWikiID() {
-	global $wgDBprefix, $wgDBname, $wgWikiID;
-	if ( $wgWikiID !== false ) {
-		return $wgWikiID;
-	} elseif ( $wgDBprefix ) {
+	global $wgDBprefix, $wgDBname;
+	if ( $wgDBprefix ) {
 		return "$wgDBname-$wgDBprefix";
 	} else {
 		return $wgDBname;