diff --git a/lib/irb/ruby-lex.rb b/lib/irb/ruby-lex.rb
index 4a700b3..fab8700 100644
--- a/lib/irb/ruby-lex.rb
+++ b/lib/irb/ruby-lex.rb
@@ -824,11 +824,11 @@ class RubyLex
 	      when "class"
 		valid = false unless peek_match?(/^\s*(<<|\w|::)/)
 	      when "def"
-		valid = false if peek_match?(/^\s*(([+\-\/*&\|^]|<<|>>|\|\||\&\&)=|\&\&|\|\|)/)
+		valid = false if peek_match?(/^\s*(([+\-\/*&\|^]|<<|>>|\|\||\&\&)=|\&\&|\|\||:)/)
 	      when "do"
-		valid = false if peek_match?(/^\s*([+\-\/*]?=|\*|<|>|\&)/)
+		valid = false if peek_match?(/^\s*([+\-\/*]?=|\*|<|>|\&|:)/)
 	      when *ENINDENT_CLAUSE
-		valid = false if peek_match?(/^\s*([+\-\/*]?=|\*|<|>|\&|\|)/)
+		valid = false if peek_match?(/^\s*([+\-\/*]?=|\*|<|>|\&|\||:)/)
 	      else
 		# no nothing
 	      end