diff --git a/env.c b/env.c
index f6f1a2862..7a7e3fe11 100644
--- a/env.c
+++ b/env.c
@@ -506,7 +506,7 @@ env_has_value(VALUE dmy, SEL sel, VALUE obj)
 }
 
 static VALUE
-env_rassoc(VALUE dmy, VALUE obj)
+env_rassoc(VALUE dmy, SEL sel, VALUE obj)
 {
     rb_secure(4);