diff --git a/src/gc.c b/src/gc.c
index 5003f4b91..ecf25d637 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -109,6 +109,7 @@ typedef struct {
     struct RRange range;
     struct RData data;
     struct RProc proc;
+    struct REnv env;
     struct RException exc;
 #ifdef MRB_WORD_BOXING
     struct RFloat floatv;