diff --git a/src/net/validator.c b/src/net/validator.c
index 52845b6e..68abe1b5 100644
--- a/src/net/validator.c
+++ b/src/net/validator.c
@@ -239,6 +239,10 @@ static int validator_start_download ( struct validator *validator,
 	/* Determine cross-signed certificate source */
 	fetch_string_setting_copy ( NULL, &crosscert_setting, &crosscert_copy );
 	crosscert = ( crosscert_copy ? crosscert_copy : crosscert_default );
+	if ( ! crosscert[0] ) {
+		rc = -EINVAL;
+		goto err_check_uri_string;
+	}
 
 	/* Allocate URI string */
 	uri_string_len = ( strlen ( crosscert ) + 22 /* "/%08x.der?subject=" */
@@ -277,6 +281,7 @@ static int validator_start_download ( struct validator *validator,
  err_open_uri_string:
 	free ( uri_string );
  err_alloc_uri_string:
+ err_check_uri_string:
 	free ( crosscert_copy );
 	return rc;
 }