diff --git a/tests/rules/test_rm_dir.py b/tests/rules/test_rm_dir.py
index 2362d0c3..d0ff324a 100644
--- a/tests/rules/test_rm_dir.py
+++ b/tests/rules/test_rm_dir.py
@@ -4,6 +4,7 @@ from thefuck.rules.rm_dir import match, get_new_command
 
 def test_match():
     assert match(Command('rm foo', '', 'rm: foo: is a directory'), None)
+    assert match(Command('rm foo', '', 'rm: foo: Is a directory'), None)
     assert not match(Command('rm foo', '', ''), None)
     assert not match(Command('rm foo', '', 'foo bar baz'), None)
     assert not match(Command('', '', ''), None)
diff --git a/thefuck/rules/rm_dir.py b/thefuck/rules/rm_dir.py
index 557278b2..89b1d2bb 100644
--- a/thefuck/rules/rm_dir.py
+++ b/thefuck/rules/rm_dir.py
@@ -5,7 +5,7 @@ from thefuck.utils import sudo_support
 @sudo_support
 def match(command, settings):
     return ('rm' in command.script
-            and 'is a directory' in command.stderr)
+            and 'is a directory' in command.stderr.lower())
 
 
 @sudo_support