Index: contrib/one-true-awk/run.c
===================================================================
--- contrib/one-true-awk/run.c
+++ contrib/one-true-awk/run.c
@@ -858,7 +858,7 @@
 		if (fmtwd < 0)
 			fmtwd = -fmtwd;
 		adjbuf(&buf, &bufsize, fmtwd+1+p-buf, recsize, &p, "format2");
-		for (t = fmt; (*t++ = *s) != '\0'; s++) {
+		for (t = fmt; *(s+1) != '\0' && (*t++ = *s) != '\0'; s++) {
 			if (!adjbuf(&fmt, &fmtsz, MAXNUMSIZE+1+t-fmt, recsize, &t, "format3"))
 				FATAL("format item %.30s... ran format() out of memory", os);
 			/* Ignore size specifiers */