Index: Parser/tokenizer.c
===================================================================
--- Parser/tokenizer.c	(revision 65848)
+++ Parser/tokenizer.c	(working copy)
@@ -448,8 +448,12 @@
 	if (io == NULL)
 		goto cleanup;
 
-	stream = PyObject_CallMethod(io, "open", "ssis",
-				     tok->filename, "r", -1, enc);
+	if (tok->filename)
+		stream = PyObject_CallMethod(io, "open", "ssis",
+					     tok->filename, "r", -1, enc);
+	else
+		stream = PyObject_CallMethod(io, "open", "isis",
+				fileno(tok->fp), "r", -1, enc);
 	if (stream == NULL)
 		goto cleanup;
 
Index: Lib/test/test_imp.py
===================================================================
--- Lib/test/test_imp.py	(revision 65848)
+++ Lib/test/test_imp.py	(working copy)
@@ -1,4 +1,5 @@
 import imp
+import sys
 import unittest
 from test import support
 
@@ -59,6 +60,21 @@
                          '"""Tokenization help for Python programs.\n')
         fp.close()
 
+    def test_issue3594(self):
+        temp_mod_name = 'test_imp_helper'
+        sys.path.insert(0, '.')
+        try:
+            with open(temp_mod_name + '.py', 'w') as file:
+                file.write("# coding: cp1252\nu = 'test.test_imp'\n")
+            file, filename, info = imp.find_module(temp_mod_name)
+            file.close()
+            self.assertEquals(file.encoding, 'cp1252')
+        finally:
+            del sys.path[0]
+            support.unlink(temp_mod_name + '.py')
+            support.unlink(temp_mod_name + '.pyc')
+            support.unlink(temp_mod_name + '.pyo')
+
     def test_reload(self):
         import marshal
         imp.reload(marshal)