diff --git a/src/string_bytes.cc b/src/string_bytes.cc
index 3f9cdf4eb15..d1ad4a1f4a9 100644
--- a/src/string_bytes.cc
+++ b/src/string_bytes.cc
@@ -296,7 +296,7 @@ size_t StringBytes::Write(Isolate* isolate,
                           enum encoding encoding,
                           int* chars_written) {
   HandleScope scope(isolate);
-  const char* data;
+  const char* data = NULL;
   size_t len = 0;
   bool is_extern = GetExternalParts(isolate, val, &data, &len);