diff --git a/pre_commit/commands/install_uninstall.py b/pre_commit/commands/install_uninstall.py
index 4698ee1e..249c87d0 100644
--- a/pre_commit/commands/install_uninstall.py
+++ b/pre_commit/commands/install_uninstall.py
@@ -9,13 +9,23 @@ import stat
 
 
 # This is used to identify the hook file we install
-IDENTIFYING_HASH = 'd8ee923c46731b42cd95cc869add4062'
+PREVIOUS_IDENTIFYING_HASHES = [
+    'd8ee923c46731b42cd95cc869add4062',
+]
+
+
+IDENTIFYING_HASH = '4d9958c90bc262f47553e2c073f14cfe'
 
 
 def is_our_pre_commit(filename):
     return IDENTIFYING_HASH in io.open(filename).read()
 
 
+def is_previous_pre_commit(filename):
+    contents = io.open(filename).read()
+    return any(hash in contents for hash in PREVIOUS_IDENTIFYING_HASHES)
+
+
 def make_executable(filename):
     original_mode = os.stat(filename).st_mode
     os.chmod(
@@ -33,7 +43,8 @@ def install(runner, overwrite=False):
     # If we have an existing hook, move it to pre-commit.legacy
     if (
         os.path.exists(runner.pre_commit_path) and
-        not is_our_pre_commit(runner.pre_commit_path)
+        not is_our_pre_commit(runner.pre_commit_path) and
+        not is_previous_pre_commit(runner.pre_commit_path)
     ):
         os.rename(runner.pre_commit_path, runner.pre_commit_legacy_path)
 
@@ -58,9 +69,17 @@ def install(runner, overwrite=False):
 
 def uninstall(runner):
     """Uninstall the pre-commit hooks."""
-    if os.path.exists(runner.pre_commit_path):
-        os.remove(runner.pre_commit_path)
-        print('pre-commit uninstalled')
+    # If our file doesn't exist or it isn't ours, gtfo.
+    if (
+        not os.path.exists(runner.pre_commit_path) or (
+            not is_our_pre_commit(runner.pre_commit_path) and
+            not is_previous_pre_commit(runner.pre_commit_path)
+        )
+    ):
+        return 0
+
+    os.remove(runner.pre_commit_path)
+    print('pre-commit uninstalled')
 
     if os.path.exists(runner.pre_commit_legacy_path):
         os.rename(runner.pre_commit_legacy_path, runner.pre_commit_path)
diff --git a/pre_commit/resources/pre-commit-hook b/pre_commit/resources/pre-commit-hook
index 60c620cf..3ddf8943 100755
--- a/pre_commit/resources/pre-commit-hook
+++ b/pre_commit/resources/pre-commit-hook
@@ -1,13 +1,17 @@
 #!/usr/bin/env bash
 # This is a randomish md5 to identify this script
-# d8ee923c46731b42cd95cc869add4062
+# 4d9958c90bc262f47553e2c073f14cfe
 
 HERE=$(dirname $(readlink -f "$0"))
 
 retv=0
 
-which pre-commit > /dev/null
-if [ $? -ne 0 ]; then
+which pre-commit >& /dev/null
+WHICH_RETV=$?
+python -c 'import pre_commit.main' >& /dev/null
+PYTHON_RETV=$?
+
+if [ $WHICH_RETV -ne 0 ] && [ $PYTHON_RETV -ne 0 ]; then
     echo '`pre-commit` not found.  Did you forget to activate your virtualenv?'
     exit 1
 fi
@@ -23,8 +27,15 @@ fi
 
 
 # Run pre-commit
-pre-commit
-if [ $? -ne 0 ]; then
+if [ $WHICH_RETV -eq 0 ]; then
+    pre-commit
+    PRE_COMMIT_RETV=$?
+else
+    python -m pre_commit.main
+    PRE_COMMIT_RETV=$?
+fi
+
+if [ $PRE_COMMIT_RETV -ne 0 ]; then
     retv=1
 fi
 
diff --git a/tests/commands/install_uninstall_test.py b/tests/commands/install_uninstall_test.py
index 4832afbb..14fafa1a 100644
--- a/tests/commands/install_uninstall_test.py
+++ b/tests/commands/install_uninstall_test.py
@@ -10,8 +10,11 @@ import subprocess
 import stat
 from plumbum import local
 
+from pre_commit.commands.install_uninstall import IDENTIFYING_HASH
+from pre_commit.commands.install_uninstall import PREVIOUS_IDENTIFYING_HASHES
 from pre_commit.commands.install_uninstall import install
 from pre_commit.commands.install_uninstall import is_our_pre_commit
+from pre_commit.commands.install_uninstall import is_previous_pre_commit
 from pre_commit.commands.install_uninstall import make_executable
 from pre_commit.commands.install_uninstall import uninstall
 from pre_commit.runner import Runner
@@ -31,6 +34,25 @@ def test_is_our_pre_commit():
     ) is True
 
 
+def test_is_not_previous_pre_commit():
+    assert is_previous_pre_commit('setup.py') is False
+
+
+def test_is_also_not_previous_pre_commit():
+    assert is_previous_pre_commit(
+        pkg_resources.resource_filename(
+            'pre_commit', 'resources/pre-commit-hook',
+        )
+    ) is False
+
+
+def test_is_previous_pre_commit(in_tmpdir):
+    with io.open('foo', 'w') as foo_file:
+        foo_file.write(PREVIOUS_IDENTIFYING_HASHES[0])
+
+    assert is_previous_pre_commit('foo')
+
+
 def test_install_pre_commit(tmpdir_factory):
     path = git_dir(tmpdir_factory)
     runner = Runner(path)
@@ -276,3 +298,43 @@ def test_uninstall_restores_legacy_hooks(tmpdir_factory):
         ret, output = _get_commit_output(tmpdir_factory, touch_file='baz')
         assert ret == 0
         assert EXISTING_COMMIT_RUN.match(output)
+
+
+def test_replace_old_commit_script(tmpdir_factory):
+    path = make_consuming_repo(tmpdir_factory, 'script_hooks_repo')
+    with local.cwd(path):
+        runner = Runner(path)
+
+        # Install a script that looks like our old script
+        pre_commit_contents = io.open(
+            pkg_resources.resource_filename(
+                'pre_commit', 'resources/pre-commit-hook',
+            )
+        ).read()
+        new_contents = pre_commit_contents.replace(
+            IDENTIFYING_HASH, PREVIOUS_IDENTIFYING_HASHES[-1],
+        )
+
+        with io.open(runner.pre_commit_path, 'w') as pre_commit_file:
+            pre_commit_file.write(new_contents)
+        make_executable(runner.pre_commit_path)
+
+        # Install normally
+        assert install(runner) == 0
+
+        ret, output = _get_commit_output(tmpdir_factory)
+        assert ret == 0
+        assert NORMAL_PRE_COMMIT_RUN.match(output)
+
+
+def test_uninstall_doesnt_remove_not_our_hooks(tmpdir_factory):
+    path = git_dir(tmpdir_factory)
+    with local.cwd(path):
+        runner = Runner(path)
+        with io.open(runner.pre_commit_path, 'w') as pre_commit_file:
+            pre_commit_file.write('#!/usr/bin/env bash\necho 1\n')
+        make_executable(runner.pre_commit_path)
+
+        assert uninstall(runner) == 0
+
+        assert os.path.exists(runner.pre_commit_path)