diff --git a/include/linux/slab.h b/include/linux/slab.h
index 6628d5e4..ef861538 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -47,10 +47,12 @@ static inline void *krealloc(void *old, size_t size, gfp_t flags)
 	if (flags & __GFP_ZERO)
 		memset(new, 0, size);
 
-	memcpy(new, old,
-	       min(malloc_usable_size(old),
-		   malloc_usable_size(new)));
-	free(old);
+	if (old) {
+		memcpy(new, old,
+		       min(malloc_usable_size(old),
+			   malloc_usable_size(new)));
+		free(old);
+	}
 
 	return new;
 }
diff --git a/tools-util.h b/tools-util.h
index 01898e21..568707bc 100644
--- a/tools-util.h
+++ b/tools-util.h
@@ -20,7 +20,9 @@
 #include <linux/uuid.h>
 #include "ccan/darray/darray.h"
 
-void die(const char *, ...);
+#define noreturn __attribute__((noreturn))
+
+void die(const char *, ...) noreturn;
 char *mprintf(const char *, ...)
 	__attribute__ ((format (printf, 1, 2)));
 void *xcalloc(size_t, size_t);