Index: WikiPage.php
===================================================================
--- WikiPage.php	(revision 114118)
+++ WikiPage.php	(working copy)
@@ -2596,10 +2596,13 @@
 		$insertRows = array();
 
 		foreach ( $insertCats as $cat ) {
-			$insertRows[] = array(
-				'cat_id' => $dbw->nextSequenceValue( 'category_cat_id_seq' ),
-				'cat_title' => $cat
-			);
+			$r = $dbw->select( 'category', 'cat_title', array( 'cat_title' => $cat ), __METHOD__ );
+			if( $r->numRows() === 0 ) {
+				$insertRows[] = array(
+					'cat_id' => $dbw->nextSequenceValue( 'category_cat_id_seq' ),
+					'cat_title' => $cat
+				);
+			}
 		}
 		$dbw->insert( 'category', $insertRows, __METHOD__, 'IGNORE' );