diff --git a/internal.h b/internal.h
index 6941586703..094e4a2462 100644
--- a/internal.h
+++ b/internal.h
@@ -996,7 +996,6 @@ ID rb_id_attrget(ID id);
 VALUE rb_proc_location(VALUE self);
 st_index_t rb_hash_proc(st_index_t hash, VALUE proc);
 int rb_block_arity(void);
-VALUE rb_block_clear_env_self(VALUE proc);
 
 /* process.c */
 #define RB_MAX_GROUPS (65536)
diff --git a/proc.c b/proc.c
index b5913d66fc..943b2ea4de 100644
--- a/proc.c
+++ b/proc.c
@@ -694,17 +694,6 @@ rb_block_lambda(void)
     return proc_new(rb_cProc, TRUE);
 }
 
-VALUE
-rb_block_clear_env_self(VALUE proc)
-{
-    rb_proc_t *po;
-    rb_env_t *env;
-    GetProcPtr(proc, po);
-    GetEnvPtr(rb_vm_proc_envval(po), env);
-    env->env[0] = Qfalse;
-    return proc;
-}
-
 /*  Document-method: ===
  *
  *  call-seq: