1 files changed, 8 insertions, 2 deletions
diff --git a/Lib/email/generator.py b/Lib/email/generator.py
index 02b4495..c480229 100644
--- a/Lib/email/generator.py
+++ b/Lib/email/generator.py
@@ -21,14 +21,20 @@ NL = '\n'
 fcre = re.compile(r'^From ', re.MULTILINE)
 
 def _is8bitstring(s):
-    if isinstance(s, str):
+    if isinstance(s, bytes):
         try:
             str(s, 'us-ascii')
+            return True
         except UnicodeError:
+            pass
+    elif isinstance(s, str):
+        try:
+            s.decode('us-ascii')
             return True
+        except UnicodeError:
+            pass
     return False
 
-
 
 class Generator:
     """Generates output from a Message object tree.