diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index adc9b1f43..274597238 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,7 @@
+2013-04-05  Corinna Vinschen  <corinna@vinschen.de>
+
+	* mmap.cc (is_mmapped_region): Call LIST_UNLOCK on premature return.
+
 2013-04-03  Corinna Vinschen  <corinna@vinschen.de>
 
 	* fhandler_proc.cc (format_proc_loadavg): Raise too small buffer size
diff --git a/winsup/cygwin/mmap.cc b/winsup/cygwin/mmap.cc
index 878fd037e..d32f6fa06 100644
--- a/winsup/cygwin/mmap.cc
+++ b/winsup/cygwin/mmap.cc
@@ -672,7 +672,10 @@ is_mmapped_region (caddr_t start_addr, caddr_t end_address)
   mmap_list *map_list = mmapped_areas.get_list_by_fd (-1, NULL);
 
   if (!map_list)
-    return false;
+    {
+      LIST_UNLOCK ();
+      return false;
+    }
 
   mmap_record *rec;
   caddr_t u_addr;