diff --git a/importlab/utils.py b/importlab/utils.py
index 1e40c01..6b508fe 100644
--- a/importlab/utils.py
+++ b/importlab/utils.py
@@ -56,7 +56,10 @@ def collect_files(path, extension):
     out = []
     # glob would be faster (see PEP471) but python glob doesn't do **/*
     for root, _, files in os.walk(path):
-        out += [os.path.join(root, f) for f in files if f.endswith(extension)]
+        if extension is None:
+            out += [os.path.join(root, f) for f in files]
+        else:
+            out += [os.path.join(root, f) for f in files if f.endswith(extension)]
     return out
 
 
@@ -66,26 +69,27 @@ def expand_source_files(filenames, cwd=None):
     This is a helper function for handling command line arguments that specify a
     list of source files and directories.
 
-    Any directories in filenames will be scanned recursively for .py files.
-    Any files that do not end with ".py" will be dropped.
+    Any directories in filenames will be scanned recursively for files.
 
     Args:
         filenames: A list of filenames to process.
         cwd: An optional working directory to expand relative paths
     Returns:
-        A list of sorted full paths to .py files
     """
     out = []
     for f in expand_paths(filenames, cwd):
         if os.path.isdir(f):
-            # If we have a directory, collect all the .py files within it.
-            out += collect_files(f, ".py")
+            # If we have a directory, collect all the files within it.
+            out += collect_files(f, None)
         else:
+            out.append(f)
+    return set(out)
             if f.endswith(".py"):
                 out.append(f)
     return sorted(set(out))
 
 
+
 def split_version(version):
     return tuple([int(v) for v in version.split('.')])