diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8b99417a..ad1cb477 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Overcommit Changelog
 
+## 0.67.1
+
+* Fix `set` gem dependency error when running with `--diff` flag
+
 ## 0.67.0
 
 * Fix bug introduced in 0.65.0 that prevented `gemfile: false` from working correctly
diff --git a/config/default.yml b/config/default.yml
index 70ae0b2d..ba8af533 100644
--- a/config/default.yml
+++ b/config/default.yml
@@ -32,6 +32,10 @@
 # your repository, and then set the `gemfile` option below to the name you gave
 # the file.
 # (Generate lock file by running `bundle install --gemfile=.overcommit_gems.rb`)
+#
+# NOTE: the following line will be parsed by a regexp rather than a proper YAML
+# parser, so avoid any values other than false or a string, and don't use inline
+# comments
 gemfile: false
 
 # Where to store hook plugins specific to a repository. These are loaded in
diff --git a/lib/overcommit/hook_context/diff.rb b/lib/overcommit/hook_context/diff.rb
index 0c4b97e0..3e9aa568 100644
--- a/lib/overcommit/hook_context/diff.rb
+++ b/lib/overcommit/hook_context/diff.rb
@@ -2,6 +2,8 @@
 
 require 'overcommit/git_repo'
 
+require 'set'
+
 module Overcommit::HookContext
   # Simulates a pre-commit context based on the diff with another git ref.
   #
diff --git a/lib/overcommit/version.rb b/lib/overcommit/version.rb
index 803dbbfc..872c5327 100644
--- a/lib/overcommit/version.rb
+++ b/lib/overcommit/version.rb
@@ -2,5 +2,5 @@
 
 # Defines the gem version.
 module Overcommit
-  VERSION = '0.67.0'
+  VERSION = '0.67.1'
 end