diff --git a/lightningd/memdump.c b/lightningd/memdump.c
index fba264e04..d2d536c23 100644
--- a/lightningd/memdump.c
+++ b/lightningd/memdump.c
@@ -73,8 +73,10 @@ static int json_add_syminfo(void *data, uintptr_t pc UNUSED,
 	struct json_result *response = data;
 	char *str;
 
-	assert(filename != NULL);
-	assert(function != NULL);
+	/* This can happen in backtraces. */
+	if (!filename || !function)
+		return 0;
+
 	str = tal_fmt(response, "%s:%u (%s)", filename, lineno, function);
 	json_add_string(response, NULL, str);
 	tal_free(str);