diff --git a/intern.h b/intern.h
index 1d74b7e22a..4cd56eac16 100644
--- a/intern.h
+++ b/intern.h
@@ -401,7 +401,7 @@ VALUE rb_cvar_defined _((VALUE, ID));
 void rb_cvar_set _((VALUE, ID, VALUE));
 VALUE rb_cvar_get _((VALUE, ID));
 VALUE rb_cvar_singleton _((VALUE));
-VALUE rb_cv_set _((VALUE, const char *, VALUE));
+void rb_cv_set _((VALUE, const char *, VALUE));
 VALUE rb_cv_get _((VALUE, const char *));
 void rb_define_class_variable _((VALUE, const char *, VALUE));
 VALUE rb_mod_class_variables _((VALUE));