diff --git a/libraries/liblutil/passwd.c b/libraries/liblutil/passwd.c
index 45f0ac661e..9bf78292c8 100644
--- a/libraries/liblutil/passwd.c
+++ b/libraries/liblutil/passwd.c
@@ -485,7 +485,7 @@ static int chk_ssha1(
 
 	rc = lutil_b64_pton(passwd->bv_val, orig_pass, passwd->bv_len);
 
-	if (rc <= sizeof(SHA1digest)) {
+	if (rc < 0 || (unsigned)rc <= sizeof(SHA1digest)) {
 		ber_memfree(orig_pass);
 		return -1;
 	}
@@ -566,7 +566,7 @@ static int chk_smd5(
 
 	rc = lutil_b64_pton(passwd->bv_val, orig_pass, passwd->bv_len);
 
-	if (rc <= sizeof(MD5digest)) {
+	if (rc < 0 || (unsigned)rc <= sizeof(MD5digest)) {
 		ber_memfree(orig_pass);
 		return -1;
 	}