Index: ext/tk/extconf.rb
===================================================================
--- ext/tk/extconf.rb	(revision 32705)
+++ ext/tk/extconf.rb	(working copy)
@@ -313,7 +313,9 @@
   paths.reverse! unless TkLib_Config["ActiveTcl"] # system has higher priority
 
   paths.map{|dir| dir.strip.chomp('/')}.each{|dir|
+    next unless File.exist?(File.join(dir, "Tcl.framework", "Headers"))
     next unless File.directory?(tcldir = File.join(dir, "Tcl.framework"))
+    next unless File.exist?(File.join(dir, "Tk.framework"), "Headers")
     next unless File.directory?(tkdir  = File.join(dir, "Tk.framework"))
     TkLib_Config["tcltk-framework"] = dir
     return [tcldir, tkdir]