diff --git a/src/ChangeLog b/src/ChangeLog
index 13f878766df..f084924ac7b 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,7 @@
 2008-09-10  Kenichi Handa  <handa@m17n.org>
 
+	* xdisp.c (handle_composition_prop): Set it->cmp_it.ch to -1.
+
 	* font.c (Ffont_shape_gstring): Make glyphs of non-nil adjustment
 	compose a grapheme cluster with the preceding base glyph.
 
diff --git a/src/xdisp.c b/src/xdisp.c
index a6d1a82eb33..314c29ee350 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -4679,6 +4679,7 @@ handle_composition_prop (it)
 
       if (it->cmp_it.id >= 0)
 	{
+	  it->cmp_it.ch = -1;
 	  it->cmp_it.nchars = COMPOSITION_LENGTH (prop);
 	  it->cmp_it.nglyphs = -1;
 	}