diff --git a/src/gbm/main/gbm.h b/src/gbm/main/gbm.h
index 2708e50a45c..8db2153e84b 100644
--- a/src/gbm/main/gbm.h
+++ b/src/gbm/main/gbm.h
@@ -35,6 +35,7 @@ extern "C" {
 
 #define __GBM__ 1
 
+#include <stddef.h>
 #include <stdint.h>
 
 /**