diff --git a/src/ChangeLog b/src/ChangeLog
index 8e6e75e8b53..3c10f66aaac 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,7 @@
+2014-08-16  Paul Eggert  <eggert@cs.ucla.edu>
+
+	* xdisp.c (set_horizontal_scroll_bar): Don't use uninitialized local.
+
 2014-08-16  Martin Rudalics  <rudalics@gmx.at>
 
 	* w32term.c (w32_horizontal_scroll_bar_handle_click): In y part
diff --git a/src/xdisp.c b/src/xdisp.c
index c46b4159de0..7553881b1f6 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -15830,7 +15830,7 @@ set_horizontal_scroll_bar (struct window *w)
 	set_buffer_internal (old_buffer);
     }
   else
-    start = end = whole = 0;
+    start = end = whole = portion = 0;
 
   w->hscroll_whole = whole;