--- gawk-3.1.7/builtin.c.orig	2010-04-01 15:52:45.000000000 +0200
+++ gawk-3.1.7/builtin.c	2010-04-01 15:57:17.000000000 +0200
@@ -1218,9 +1218,18 @@ check_pos:
 			if (fw == 0 && ! have_prec)
 				;
 			else if (gawk_mb_cur_max > 1 && (cs1 == 's' || cs1 == 'c')) {
+				int nchars_needed = 0;
+
 				assert(cp == arg->stptr || cp == cpbuf);
-				copy_count = mbc_byte_count(arg->stptr,
-						cs1 == 's' ? arg->stlen : 1);
+
+				if (cs1 == 'c')
+					nchars_needed = 1;
+				else if (have_prec)
+					nchars_needed = prec;
+				else
+					nchars_needed = arg->stlen;
+
+				copy_count = mbc_byte_count(arg->stptr, nchars_needed);
 			}
 			bchunk(cp, copy_count);
 			while (fw > prec) {