diff --git a/lib/piston/forms.py b/lib/piston/forms.py
index 351df7c..28b3af3 100644
--- a/lib/piston/forms.py
+++ b/lib/piston/forms.py
@@ -50,6 +50,7 @@ class OAuthAuthenticationForm(forms.Form):
     @staticmethod
     def get_csrf_signature(key, token):
         # Check signature...
+        key.encode('ascii')
         try:
             import hashlib # 2.5
             hashed = hmac.new(key, token, hashlib.sha1)
diff --git a/lib/piston/oauth.py b/lib/piston/oauth.py
index 3a42e20..62bece7 100644
--- a/lib/piston/oauth.py
+++ b/lib/piston/oauth.py
@@ -620,6 +620,7 @@ class OAuthSignatureMethod_HMAC_SHA1(OAuthSignatureMethod):
         key, raw = self.build_signature_base_string(oauth_request, consumer,
             token)
 
+        key.encode('ascii')
         # HMAC object.
         try:
             import hashlib # 2.5
@@ -647,4 +648,4 @@ class OAuthSignatureMethod_PLAINTEXT(OAuthSignatureMethod):
     def build_signature(self, oauth_request, consumer, token):
         key, raw = self.build_signature_base_string(oauth_request, consumer,
             token)
-        return key
\ No newline at end of file
+        return key