diff --git a/pb_encode.c b/pb_encode.c
index 2ad9925..6fcbfa6 100644
--- a/pb_encode.c
+++ b/pb_encode.c
@@ -68,7 +68,7 @@
     /* In PB_BUFFER_ONLY configuration the callback pointer is just int*.
      * NULL pointer marks a sizing field, so put a non-NULL value to mark a buffer stream.
      */
-    static const int marker;
+    static const int marker = 0;
     stream.callback = &marker;
 #else
     stream.callback = &buf_write;