diff --git a/cmd/sf.c b/cmd/sf.c
index f971eec..e7ff9a6 100644
--- a/cmd/sf.c
+++ b/cmd/sf.c
@@ -287,7 +287,7 @@
 	}
 
 	buf = map_physmem(addr, len, MAP_WRBACK);
-	if (!buf) {
+	if (!buf && addr) {
 		puts("Failed to map physical memory\n");
 		return 1;
 	}