diff --git a/path.c b/path.c
index e50d2befcf..1ca2cf9a28 100644
--- a/path.c
+++ b/path.c
@@ -661,6 +661,10 @@ int validate_headref(const char *path)
 	len = read_in_full(fd, buffer, sizeof(buffer)-1);
 	close(fd);
 
+	if (len < 0)
+		return -1;
+	buffer[len] = '\0';
+
 	/*
 	 * Is it a symbolic ref?
 	 */