diff --git a/bin/tests/system/rpz/testlib/test-data.c b/bin/tests/system/rpz/testlib/test-data.c
index 8ccebd6579..7d3c625f7b 100644
--- a/bin/tests/system/rpz/testlib/test-data.c
+++ b/bin/tests/system/rpz/testlib/test-data.c
@@ -865,8 +865,8 @@ apply_update(const char *updstr, trpz_result_t **presults, size_t *pnresults,
 		}
 
 	} else if (!strcasecmp(rrbuf, "TXT")) {
-		char *ftext = NULL;
-
+		const char *ftext = NULL;
+		size_t len;
 		ftext = strstr(updstr, databuf);
 		if (ftext == NULL) {
 			fprintf(stderr, "Error parsing TXT record: \"%s\"\n",
@@ -875,15 +875,19 @@ apply_update(const char *updstr, trpz_result_t **presults, size_t *pnresults,
 		}
 
 		if (*ftext == '"') {
-			*ftext++ = 0;
+			ftext++;
 
-			if (ftext[strlen(ftext) - 1] == '"') {
-				ftext[strlen(ftext) - 1] = 0;
+			len = strlen(ftext);
+			if (len > 0 && ftext[len - 1] == '"') {
+				len--;
 			}
+		} else {
+			len = strlen(ftext);
 		}
 
-		strncpy(databuf, ftext, sizeof(databuf));
-		databuf[sizeof(databuf) - 1] = 0;
+		strncpy(databuf, ftext,
+			len < sizeof(databuf) ? len : sizeof(databuf));
+		databuf[len < sizeof(databuf) ? len : sizeof(databuf) - 1] = 0;
 		policy = LIBRPZ_POLICY_RECORD;
 	} else if (!strcasecmp(rrbuf, "DNAME")) {
 		policy = LIBRPZ_POLICY_RECORD;