diff --git a/ChangeLog b/ChangeLog
index b3c9892466..c0f7f5d008 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2015-08-20  Florian Weimer  <fweimer@redhat.com>
+
+	* sysdeps/x86/elide.h (ELIDE_UNLOCK): Document crash due to
+	incorrect use.
+
 2015-08-19  Joseph Myers  <joseph@codesourcery.com>
 
 	[BZ #18370]
diff --git a/sysdeps/x86/elide.h b/sysdeps/x86/elide.h
index 47e89cfc8d..6e53288340 100644
--- a/sysdeps/x86/elide.h
+++ b/sysdeps/x86/elide.h
@@ -93,7 +93,9 @@ elision_adapt(signed char *adapt_count, unsigned int status)
     ret;						\
     })
 
-/* Returns true if lock defined by IS_LOCK_FREE was elided.  */
+/* Returns true if lock defined by IS_LOCK_FREE was elided.  The call
+   to _xend crashes if the application incorrectly tries to unlock a
+   lock which has not been locked.  */
 
 #define ELIDE_UNLOCK(is_lock_free)		\
   ({						\