diff --git a/ChangeLog b/ChangeLog
index b35833af0e..658708f718 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat Jan 28 05:53:34 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/irb/completion.rb (IRB::InputCompletor::CompletionProc):
+	  ignore non-string name modules.  [ruby-core:42244][Bug #5938]
+
 Fri Jan 27 16:31:45 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* gc.c (HEAP_ALIGN, HEAP_ALIGN_MASK): DRY, let compiler calculate
diff --git a/lib/irb/completion.rb b/lib/irb/completion.rb
index 54e6526957..7fd69a0a09 100644
--- a/lib/irb/completion.rb
+++ b/lib/irb/completion.rb
@@ -178,8 +178,12 @@ module IRB
 	    rescue Exception
 	      name = ""
 	    end
-	    next if name != "IRB::Context" and
-	      /^(IRB|SLex|RubyLex|RubyToken)/ =~ name
+            begin
+              next if name != "IRB::Context" and
+                /^(IRB|SLex|RubyLex|RubyToken)/ =~ name
+            rescue Exception
+              next
+            end
 	    candidates.concat m.instance_methods(false).collect{|x| x.to_s}
 	  }
 	  candidates.sort!
diff --git a/test/irb/test_completion.rb b/test/irb/test_completion.rb
new file mode 100644
index 0000000000..3c11eb003c
--- /dev/null
+++ b/test/irb/test_completion.rb
@@ -0,0 +1,17 @@
+require 'test/unit'
+require_relative '../ruby/envutil'
+
+module TestIRB
+  class TestCompletion < Test::Unit::TestCase
+    def test_nonstring_module_name
+      bug5938 = '[ruby-core:42244]'
+      cmds = %W[-rirb -rirb/completion -e IRB.setup(__FILE__)
+       -e IRB.conf[:MAIN_CONTEXT]=IRB::Irb.new.context
+       -e module\sFoo;def\sself.name;//;end;end
+       -e IRB::InputCompletor::CompletionProc.call("[1].first.")
+       -- -f --]
+      status = assert_in_out_err(cmds, "", //, [], bug5938)
+      assert(status.success?, bug5938)
+    end
+  end
+end