diff --git a/include/msgpack/fbuffer.h b/include/msgpack/fbuffer.h
index d766c839..d478008c 100644
--- a/include/msgpack/fbuffer.h
+++ b/include/msgpack/fbuffer.h
@@ -25,7 +25,7 @@ extern "C" {
 
 static inline int msgpack_fbuffer_write(void* data, const char* buf, size_t len)
 {
-    return (len == fwrite(buf, len, 1, (FILE *)data)) ? 0 : -1;
+    return (1 == fwrite(buf, len, 1, (FILE *)data)) ? 0 : -1;
 }
 
 /** @} */