Index: ChangeLog
===================================================================
--- ChangeLog	(revision 42019)
+++ ChangeLog	(working copy)
@@ -1,3 +1,7 @@
+Wed Jul 17 04:56:29 2013  Matthew M. Boedicker  <matthewm@boedicker.org>
+
+	* hash.c (env_fetch): Add key name to message on ENV.fetch KeyError.
+
 Wed Jul 17 12:30:05 2013  Tanaka Akira  <akr@fsij.org>
 
 	* include/ruby/st.h (st_strcasecmp): Macro defined for compatibility.
Index: hash.c
===================================================================
--- hash.c	(revision 42019)
+++ hash.c	(working copy)
@@ -2411,7 +2411,7 @@
     if (!env) {
 	if (block_given) return rb_yield(key);
 	if (argc == 1) {
-	    rb_raise(rb_eKeyError, "key not found");
+	    rb_raise(rb_eKeyError, "key not found: \"%s\"", nam);
 	}
 	return if_none;
     }
Index: test/ruby/test_env.rb
===================================================================
--- test/ruby/test_env.rb	(revision 42019)
+++ test/ruby/test_env.rb	(working copy)
@@ -103,7 +103,9 @@
     ENV["test"] = "foo"
     assert_equal("foo", ENV.fetch("test"))
     ENV.delete("test")
-    assert_raise(KeyError) { ENV.fetch("test") }
+    assert_raise_with_message(KeyError, 'key not found: "test"') do
+      ENV.fetch("test")
+    end
     assert_equal("foo", ENV.fetch("test", "foo"))
     assert_equal("bar", ENV.fetch("test") { "bar" })
     assert_equal("bar", ENV.fetch("test", "foo") { "bar" })