diff --git a/include/rabit/c_api.h b/include/rabit/c_api.h
index 16db693b4..a05ebd4d2 100644
--- a/include/rabit/c_api.h
+++ b/include/rabit/c_api.h
@@ -11,6 +11,7 @@
 #define RABIT_EXTERN_C extern "C"
 #include <cstdio>
 #else
+#define RABIT_EXTERN_C
 #include <stdio.h>
 #endif