diff --git a/pre_commit/git.py b/pre_commit/git.py
index 75e2662c..4d03c26a 100644
--- a/pre_commit/git.py
+++ b/pre_commit/git.py
@@ -7,13 +7,13 @@ import os.path
 import re
 from plumbum import local
 
+from pre_commit.errors import FatalError
 from pre_commit.util import memoize_by_cwd
 
 
 logger = logging.getLogger('pre_commit')
 
 
-@memoize_by_cwd
 def get_root():
     path = os.getcwd()
     while len(path) > 1:
@@ -21,7 +21,10 @@ def get_root():
             return path
         else:
             path = os.path.normpath(os.path.join(path, '../'))
-    raise AssertionError('called from outside of the gits')
+    raise FatalError(
+        'Called from outside of the gits. '
+        'Please cd to a git repository.'
+    )
 
 
 def is_in_merge_conflict():
diff --git a/tests/git_test.py b/tests/git_test.py
index 9b22359d..c3b728a6 100644
--- a/tests/git_test.py
+++ b/tests/git_test.py
@@ -6,6 +6,7 @@ import pytest
 from plumbum import local
 
 from pre_commit import git
+from pre_commit.errors import FatalError
 from testing.fixtures import git_dir
 
 
@@ -24,6 +25,12 @@ def test_get_root_deeper(tmpdir_factory):
         assert git.get_root() == path
 
 
+def test_get_root_not_git_dir(tmpdir_factory):
+    with local.cwd(tmpdir_factory.get()):
+        with pytest.raises(FatalError):
+            git.get_root()
+
+
 def test_is_not_in_merge_conflict(tmpdir_factory):
     path = git_dir(tmpdir_factory)
     with local.cwd(path):