diff --git a/src/flake8/checker.py b/src/flake8/checker.py
index 569eafa..6e53cb5 100644
--- a/src/flake8/checker.py
+++ b/src/flake8/checker.py
@@ -209,6 +209,7 @@ class Manager(object):
 
         filename_patterns = self.options.filename
         running_from_vcs = self.options._running_from_vcs
+        running_from_diff = self.options.diff
 
         # NOTE(sigmavirus24): Yes this is a little unsightly, but it's our
         # best solution right now.
@@ -227,6 +228,7 @@ class Manager(object):
             # If it was specified explicitly, the user intended for it to be
             # checked.
             explicitly_provided = (not running_from_vcs and
+                                   not running_from_diff and
                                    (argument == filename))
             return ((file_exists and
                      (explicitly_provided or matches_filename_patterns)) or