Index: wp-includes/class.wp-scripts.php
===================================================================
--- wp-includes/class.wp-scripts.php	(revision 18341)
+++ wp-includes/class.wp-scripts.php	(working copy)
@@ -122,10 +122,16 @@
 			$src = add_query_arg('ver', $ver, $src);
 		$src = esc_url(apply_filters( 'script_loader_src', $src, $handle ));
 
-		if ( $this->do_concat )
+		if ( $this->do_concat ) {
 			$this->print_html .= "<script type='text/javascript' src='$src'></script>\n";
-		else
-			echo "<script type='text/javascript' src='$src'></script>\n";
+		} else {
+			$start_cond = $end_cond = '';
+			if ( isset($this->registered[$handle]->extra['conditional']) && $this->registered[$handle]->extra['conditional'] ) {
+				$start_cond = "<!--[if {$this->registered[$handle]->extra['conditional']}]>\n";
+				$end_cond = "<![endif]-->\n";
+			}
+			echo "{$start_cond}<script type='text/javascript' src='$src'></script>\n{$end_cond}";
+		}
 
 		return true;
 	}