diff --git a/include/mruby/proc.h b/include/mruby/proc.h
index 9c2666289..5a6741610 100644
--- a/include/mruby/proc.h
+++ b/include/mruby/proc.h
@@ -30,7 +30,7 @@ struct REnv {
 #define MRB_ENV_UNSHARE_STACK(e) ((e)->cioff = -1)
 #define MRB_ENV_STACK_SHARED_P(e) ((e)->cioff >= 0)
 
-MRB_API void mrb_env_unshare(mrb_state*, struct REnv*);
+void mrb_env_unshare(mrb_state*, struct REnv*);
 
 struct RProc {
   MRB_OBJECT_HEADER;
diff --git a/src/vm.c b/src/vm.c
index b5a2aa7bf..196b2934e 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -273,7 +273,7 @@ cipush(mrb_state *mrb)
   return ci;
 }
 
-MRB_API void
+void
 mrb_env_unshare(mrb_state *mrb, struct REnv *e)
 {
   if (e == NULL) return;