diff --git a/lib/reline.rb b/lib/reline.rb
index 210f33478fd831..a128d7347db85c 100644
--- a/lib/reline.rb
+++ b/lib/reline.rb
@@ -166,9 +166,13 @@ def dig_perfect_match_proc=(p)
 
     DialogProc = Struct.new(:dialog_proc, :context)
     def add_dialog_proc(name_sym, p, context = nil)
-      raise ArgumentError unless p.respond_to?(:call) or p.nil?
       raise ArgumentError unless name_sym.instance_of?(Symbol)
-      @dialog_proc_list[name_sym] = DialogProc.new(p, context)
+      if p.nil?
+        @dialog_proc_list.delete(name_sym)
+      else
+        raise ArgumentError unless p.respond_to?(:call)
+        @dialog_proc_list[name_sym] = DialogProc.new(p, context)
+      end
     end
 
     def dialog_proc(name_sym)
diff --git a/test/reline/test_reline.rb b/test/reline/test_reline.rb
index 9692605a007eb7..460fb7872d5b18 100644
--- a/test/reline/test_reline.rb
+++ b/test/reline/test_reline.rb
@@ -321,6 +321,9 @@ def test_add_dialog_proc
     d = Reline.dialog_proc(:test_proc)
     assert_equal(dummy_proc_2, d.dialog_proc)
 
+    Reline.add_dialog_proc(:test_proc, nil)
+    assert_nil(Reline.dialog_proc(:test_proc))
+
     l = lambda {}
     Reline.add_dialog_proc(:test_lambda, l)
     d = Reline.dialog_proc(:test_lambda)