Index: boot/generic/src/payload.c
===================================================================
--- boot/generic/src/payload.c	(revision 145a13b720625fa3339311792a3a0793509d1d18)
+++ boot/generic/src/payload.c	(revision df7dc9e565c0538447fbaaec2d4e67c593d48512)
@@ -61,5 +61,5 @@
 {
 	char *e = (char *) ext(s);
-	if (str_cmp(e, ".gz") == 0)
+	if (e != NULL && str_cmp(e, ".gz") == 0)
 		*e = '\0';
 }
@@ -67,5 +67,6 @@
 static bool isgzip(const char *s)
 {
-	return str_cmp(ext(s), ".gz") == 0;
+	const char *e = ext(s);
+	return e != NULL && str_cmp(e, ".gz") == 0;
 }