diff --git a/blib2to3/pgen2/tokenize.py b/blib2to3/pgen2/tokenize.py
index 9a7664b..1f51ff0 100644
--- a/blib2to3/pgen2/tokenize.py
+++ b/blib2to3/pgen2/tokenize.py
@@ -516,13 +516,14 @@ def generate_tokens(readline):
                         stashed = tok
                         continue
 
-                    if token == 'def':
+                    if token in ('def', 'for'):
                         if (stashed
                                 and stashed[0] == NAME
                                 and stashed[1] == 'async'):
 
-                            async_def = True
-                            async_def_indent = indents[-1]
+                            if token == 'def':
+                                async_def = True
+                                async_def_indent = indents[-1]
 
                             yield (ASYNC, stashed[1],
                                    stashed[2], stashed[3],
diff --git a/tests/data/python37.py b/tests/data/python37.py
new file mode 100644
index 0000000..ae20ade
--- /dev/null
+++ b/tests/data/python37.py
@@ -0,0 +1,13 @@
+#!/usr/bin/env python3.7
+
+def f():
+    return (i*2 async for i in arange(42))
+
+# output
+
+
+#!/usr/bin/env python3.7
+
+
+def f():
+    return (i * 2 async for i in arange(42))
diff --git a/tests/test_black.py b/tests/test_black.py
index 10d7f28..9c798ca 100644
--- a/tests/test_black.py
+++ b/tests/test_black.py
@@ -411,6 +411,16 @@ def test_stub(self) -> None:
         self.assertFormatEqual(expected, actual)
         black.assert_stable(source, actual, line_length=ll, mode=mode)
 
+    @patch("black.dump_to_file", dump_to_stderr)
+    def test_python37(self) -> None:
+        source, expected = read_data("python37")
+        actual = fs(source)
+        self.assertFormatEqual(expected, actual)
+        major, minor = sys.version_info[:2]
+        if major > 3 or (major == 3 and minor >= 7):
+            black.assert_equivalent(source, actual)
+        black.assert_stable(source, actual, line_length=ll)
+
     @patch("black.dump_to_file", dump_to_stderr)
     def test_fmtonoff(self) -> None:
         source, expected = read_data("fmtonoff")