Index: wp-includes/meta.php
===================================================================
--- wp-includes/meta.php	(revision 18407)
+++ wp-includes/meta.php	(working copy)
@@ -422,11 +422,16 @@
 
 		$this->queries = array();
 
-		foreach ( $meta_query as $key => $query ) {
-			if ( ! is_array( $query ) )
-				continue;
-
-			$this->queries[] = $query;
+		// Single meta queries don't need to pass an array of arrays
+		if( isset( $meta_query['key'] ) || isset( $meta_query['value'] ) ) {
+			$this->queries[] = $meta_query;
+		} else {
+			foreach ( $meta_query as $key => $query ) {
+				if ( ! is_array( $query ) )
+					continue;
+	
+				$this->queries[] = $query;
+			}
 		}
 	}