diff --git a/pywb/warcserver/inputrequest.py b/pywb/warcserver/inputrequest.py
index 2ee3cd7d..f910d2e3 100644
--- a/pywb/warcserver/inputrequest.py
+++ b/pywb/warcserver/inputrequest.py
@@ -228,9 +228,18 @@ class MethodQueryCanonicalizer(object):
         if not mime:
             mime = ''
 
-        if mime.startswith('application/x-www-form-urlencoded'):
+        def handle_binary(query):
+            query = base64.b64encode(query)
             query = to_native_str(query)
-            query = unquote_plus(query)
+            query = '__wb_post_data=' + query
+            return query
+
+        if mime.startswith('application/x-www-form-urlencoded'):
+            try:
+                query = to_native_str(query.decode('utf-8'))
+                query = unquote_plus(query)
+            except UnicodeDecodeError:
+                query = handle_binary(query)
 
         elif mime.startswith('multipart/'):
             env = {'REQUEST_METHOD': 'POST',
@@ -256,9 +265,7 @@ class MethodQueryCanonicalizer(object):
             query = self.amf_parse(query, environ)
 
         else:
-            query = base64.b64encode(query)
-            query = to_native_str(query)
-            query = '__wb_post_data=' + query
+            query = handle_binary(query)
 
         self.query = query
 
diff --git a/pywb/warcserver/test/test_inputreq.py b/pywb/warcserver/test/test_inputreq.py
index b4f275ac..fe5cf67c 100644
--- a/pywb/warcserver/test/test_inputreq.py
+++ b/pywb/warcserver/test/test_inputreq.py
@@ -83,6 +83,7 @@ class TestPostQueryExtract(object):
     @classmethod
     def setup_class(cls):
         cls.post_data = b'foo=bar&dir=%2Fbaz'
+        cls.binary_post_data = b'\x816l`L\xa04P\x0e\xe0r\x02\xb5\x89\x19\x00fP\xdb\x0e\xb0\x02,'
 
     def test_post_extract_1(self):
         mq = MethodQueryCanonicalizer('POST', 'application/x-www-form-urlencoded',
@@ -135,6 +136,13 @@ class TestPostQueryExtract(object):
 
         assert mq.append_query('http://example.com/') == 'http://example.com/?foo=bar&dir=/baz'
 
+    def test_post_extract_malformed_form_data(self):
+        mq = MethodQueryCanonicalizer('POST', 'application/x-www-form-urlencoded',
+                                len(self.binary_post_data), BytesIO(self.binary_post_data))
+
+        #base64 encoded data
+        assert mq.append_query('http://example.com/') == 'http://example.com/?__wb_post_data=gTZsYEygNFAO4HICtYkZAGZQ2w6wAiw='
+
     def test_options(self):
         mq = MethodQueryCanonicalizer('OPTIONS', '', 0, BytesIO())
         assert mq.append_query('http://example.com/') == 'http://example.com/?__pywb_method=options'