diff --git a/src/intervals.c b/src/intervals.c
index 3c67f215aa6..3e970797ebe 100644
--- a/src/intervals.c
+++ b/src/intervals.c
@@ -49,6 +49,8 @@ the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
 
 /* Factor for weight-balancing interval trees.  */
 Lisp_Object interval_balance_threshold;
+
+Lisp_Object merge_properties_sticky ();
 
 /* Utility functions for intervals.  */