diff --git a/include/mruby/internal.h b/include/mruby/internal.h
index b251c72f0..ac5ecfbc2 100644
--- a/include/mruby/internal.h
+++ b/include/mruby/internal.h
@@ -110,6 +110,7 @@ void mrb_rational_copy(mrb_state *mrb, mrb_value x, mrb_value y);
 struct RProc *mrb_closure_new(mrb_state*, const mrb_irep*);
 void mrb_proc_copy(mrb_state *mrb, struct RProc *a, struct RProc *b);
 mrb_int mrb_proc_arity(const struct RProc *p);
+struct REnv *mrb_env_new(mrb_state *mrb, struct mrb_context *c, mrb_callinfo *ci, int nstacks, mrb_value *stack, struct RClass *tc);
 #endif
 
 /* range */
diff --git a/mrbgems/mruby-eval/src/eval.c b/mrbgems/mruby-eval/src/eval.c
index 389c1bf4d..19145300e 100644
--- a/mrbgems/mruby-eval/src/eval.c
+++ b/mrbgems/mruby-eval/src/eval.c
@@ -9,8 +9,6 @@
 #include <mruby/variable.h>
 #include <mruby/internal.h>
 
-struct REnv *mrb_env_new(mrb_state *mrb, struct mrb_context *c, mrb_callinfo *ci, int nstacks, mrb_value *stack, struct RClass *tc);
-
 static struct RProc*
 create_proc_from_string(mrb_state *mrb, const char *s, mrb_int len, mrb_value binding, const char *file, mrb_int line)
 {