diff --git a/src/ChangeLog b/src/ChangeLog
index 637164281d4..4991d74135b 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2014-01-11  K. Handa  <handa@gnu.org>
+
+	* composite.c (composition_update_it): Fix indexing of
+	LGSTRING_CHAR (Bug#15984).
+
 2014-01-11  Fabrice Popineau  <fabrice.popineau@gmail.com>
 
 	* unexw32.c (_start) [__MINGW64__]: Define to __start.
diff --git a/src/composite.c b/src/composite.c
index 367fc8e3f9f..40cef814c1d 100644
--- a/src/composite.c
+++ b/src/composite.c
@@ -1412,7 +1412,7 @@ composition_update_it (struct composition_it *cmp_it, ptrdiff_t charpos, ptrdiff
       cmp_it->width = 0;
       for (i = cmp_it->nchars - 1; i >= 0; i--)
 	{
-	  c = XINT (LGSTRING_CHAR (gstring, i));
+	  c = XINT (LGSTRING_CHAR (gstring, cmp_it->from + i));
 	  cmp_it->nbytes += CHAR_BYTES (c);
 	  cmp_it->width += CHAR_WIDTH (c);
 	}