Index: src/chars.c
===================================================================
--- src/chars.c	(revision 5143)
+++ src/chars.c	(working copy)
@@ -488,6 +488,20 @@
 
     assert(buf != NULL && pos <= strlen(buf));
 
+#ifdef ENABLE_UTF8
+    if (use_utf8) {
+	if (mblen(buf + pos - 1, MB_CUR_MAX) > 0)
+	    return pos - 1;
+	if (mblen(buf + pos - 2, MB_CUR_MAX) > 0)
+	    return pos - 2;
+	if (mblen(buf + pos - 3, MB_CUR_MAX) > 0)
+	    return pos - 3;
+	if (mblen(buf + pos - 4, MB_CUR_MAX) > 0)
+	    return pos - 4;
+	else
+	    return pos - 1;
+    }
+#endif
     /* There is no library function to move backward one multibyte
      * character.  Here is the naive, O(pos) way to do it. */
     while (before < pos) {