diff --git a/ext/tk/sample/tkalignbox.rb b/ext/tk/sample/tkalignbox.rb
index 9936929e35..cca91c9b0d 100644
--- a/ext/tk/sample/tkalignbox.rb
+++ b/ext/tk/sample/tkalignbox.rb
@@ -20,12 +20,12 @@ class TkAlignBox < TkFrame
   end
 
   def _set_framesize
-    fail RuntimeError, "TkAlignBox is an abstruct class"
+    fail RuntimeError, "TkAlignBox is an abstract class"
   end
   private :_set_framesize
 
   def _place_config(widget, idx, cnt)
-    fail RuntimeError, "TkAlignBox is an abstruct class"
+    fail RuntimeError, "TkAlignBox is an abstract class"
   end
   private :_place_config