diff --git a/ext/tk/lib/tkcanvas.rb b/ext/tk/lib/tkcanvas.rb
index 47e925c4fe..a899c9caaf 100644
--- a/ext/tk/lib/tkcanvas.rb
+++ b/ext/tk/lib/tkcanvas.rb
@@ -548,7 +548,7 @@ class TkcTag<TkObject
     @path = @id = Tk_CanvasTag_ID.join
     CTagID_TBL[@cpath] = {} unless CTagID_TBL[@cpath]
     CTagID_TBL[@cpath][@id] = self
-    Tk_CanvasTag_ID[1] = Tk_CanvasTag_ID[1].succ
+    Tk_CanvasTag_ID[1].succ!
     if mode
       tk_call @c.path, "addtag", @id, mode, *args
     end
@@ -670,7 +670,7 @@ class TkcGroup<TkcTag
     @path = @id = Tk_cGroup_ID.join
     CTagID_TBL[@cpath] = {} unless CTagID_TBL[@cpath]
     CTagID_TBL[@cpath][@id] = self
-    Tk_cGroup_ID[1] = Tk_cGroup_ID[1].succ
+    Tk_cGroup_ID[1].succ!
     add(*args) if args != []
   end
   
@@ -829,7 +829,7 @@ class TkImage<TkObject
 
   def initialize(keys=nil)
     @path = Tk_Image_ID.join
-    Tk_Image_ID[1] = Tk_Image_ID[1].succ
+    Tk_Image_ID[1].succ!
     tk_call 'image', 'create', @type, @path, *hash_kv(keys)
     Tk_IMGTBL[@path] = self
   end
diff --git a/ext/tk/lib/tktext.rb b/ext/tk/lib/tktext.rb
index 6fa69aa597..ae40ac8750 100644
--- a/ext/tk/lib/tktext.rb
+++ b/ext/tk/lib/tktext.rb
@@ -991,7 +991,7 @@ class TkTextMark<TkObject
     TMarkID_TBL[@id] = self
     TMarkID_TBL[@tpath] = {} unless TMarkID_TBL[@tpath]
     TMarkID_TBL[@tpath][@id] = self
-    Tk_TextMark_ID[0] = Tk_TextMark_ID[0].succ
+    Tk_TextMark_ID[1].succ!
     tk_call @t.path, 'mark', 'set', @id, index
     @t._addtag id, self
   end