Ripped from Debian's gawk_3.1.5.dfsg-4.diff.gz

#! /bin/sh -e
## 20_eval.c-utf-8-strcat.dpatch
##
## DP: Description: Fix handling of string concatenation with multi-byte strings. (#347490)
## DP: Author: Karel Zak and Aharon Robbins
## DP: Upstream status: Unclear - in discussion
## DP: URL: http://lists.gnu.org/archive/html/bug-gnu-utils/2006-02/msg00023.html
## DP: Date: 2006-02-10

if [ $# -lt 1 ]; then
    echo "`basename $0`: script expects -patch|-unpatch as argument" >&2
    exit 1
fi

[ -f debian/patches/00patch-opts ] && . debian/patches/00patch-opts
patch_opts="${patch_opts:--f --no-backup-if-mismatch} ${2:+-d $2}"

case "$1" in
    -patch) patch -p1 ${patch_opts} < $0;;
    -unpatch) patch -R -p1 ${patch_opts} < $0;;
    *)
        echo "`basename $0`: script expects -patch|-unpatch as argument" >&2
        exit 1;;
esac

exit 0

@DPATCH@
diff -urNad --exclude=CVS --exclude=.svn ./eval.c /tmp/dpep-work.D8ZI7f/gawk-3.1.5/eval.c
--- ./eval.c	2006-04-18 03:07:14.000000000 +0100
+++ /tmp/dpep-work.D8ZI7f/gawk-3.1.5/eval.c	2006-04-18 03:07:52.000000000 +0100
@@ -1176,6 +1176,13 @@
 			memcpy(l->stptr + l->stlen, r->stptr, r->stlen);
 			l->stlen += r->stlen;
 			l->stptr[l->stlen] = '\0';
+#if defined MBS_SUPPORT
+			if (l->wstptr != NULL)
+				free(l->wstptr);
+				l->wstptr = NULL;
+				l->wstlen = 0;
+				l->flags &= ~WSTRCUR;
+#endif /* MBS_SUPPORT */
 		} else {
 			char *nval;
 			size_t nlen = l->stlen + r->stlen + 2;