-if(isset($wgExtraNamespaces)) {
- $wgCanonicalNamespaceNames=$wgCanonicalNamespaceNames+$wgExtraNamespaces;
+if( defined( 'MEDIAWIKI' ) && is_array( $wgExtraNamespaces ) ) {
+ $wgCanonicalNamespaceNames = $wgCanonicalNamespaceNames + $wgExtraNamespaces;