diff --git a/src/flake8/checker.py b/src/flake8/checker.py
index f7bd540..d5132ff 100644
--- a/src/flake8/checker.py
+++ b/src/flake8/checker.py
@@ -237,6 +237,12 @@ class Manager(object):
         exclude = self.options.exclude
         if not exclude:
             return False
+        if path == '-':
+            # stdin, use display name to check exclusion, if present
+            path = self.options.stdin_display_name
+            if path is None:
+                LOG.debug("unnamed stdin has not been excluded")
+                return False
         basename = os.path.basename(path)
         if utils.fnmatch(basename, exclude):
             LOG.debug('"%s" has been excluded', basename)
@@ -263,12 +269,11 @@ class Manager(object):
         # best solution right now.
         def should_create_file_checker(filename):
             """Determine if we should create a file checker."""
-            matches_filename_patterns = utils.fnmatch(
-                filename, filename_patterns
+            return (
+                filename == '-' or  # stdin
+                utils.fnmatch(filename, filename_patterns) and
+                os.path.exists(filename)
             )
-            is_stdin = filename == '-'
-            file_exists = os.path.exists(filename)
-            return (file_exists and matches_filename_patterns) or is_stdin
 
         self.checkers = [
             FileChecker(filename, self.checks, self.style_guide)
diff --git a/src/flake8/utils.py b/src/flake8/utils.py
index 68ed530..52417fc 100644
--- a/src/flake8/utils.py
+++ b/src/flake8/utils.py
@@ -208,24 +208,26 @@ def filenames_from(arg, predicate=None):
     """
     if predicate is None:
         predicate = _default_predicate
-    if os.path.isdir(arg):
-        for root, sub_directories, files in os.walk(arg):
-            if predicate(root):
-                sub_directories[:] = []
-                continue
 
+    if predicate(arg):
+        return
+
+    if arg == "-":
+        # stdin, don't call isdir()
+        yield arg
+    elif os.path.isdir(arg):
+        for root, sub_directories, files in os.walk(arg):
             # NOTE(sigmavirus24): os.walk() will skip a directory if you
             # remove it from the list of sub-directories.
-            for directory in sub_directories:
-                joined = os.path.join(root, directory)
-                if predicate(directory) or predicate(joined):
-                    sub_directories.remove(directory)
+            sub_directories[:] = [
+                directory for directory in sub_directories
+                if not predicate(os.path.join(root, directory))
+            ]
 
             for filename in files:
                 joined = os.path.join(root, filename)
-                if predicate(joined) or predicate(filename):
-                    continue
-                yield joined
+                if not predicate(joined):
+                    yield joined
     else:
         yield arg