diff --git a/consulate/api/base.py b/consulate/api/base.py
index b870312..c5c4ae4 100644
--- a/consulate/api/base.py
+++ b/consulate/api/base.py
@@ -131,7 +131,10 @@ def _demarshal(self, body):
                 return None
             try:
                 if utils.PYTHON3 and isinstance(body, bytes):
-                    body = body.decode('utf-8')
+                    try:
+                        body = body.decode('utf-8')
+                    except UnicodeDecodeError:
+                        pass
                 value = json.loads(body, encoding='utf-8')
             except (TypeError, ValueError):
                 return body
@@ -143,7 +146,10 @@ def _demarshal(self, body):
                         try:
                             row['Value'] = base64.b64decode(row['Value'])
                             if isinstance(row['Value'], bytes):
-                                row['Value'] = row['Value'].decode('utf-8')
+                                try:
+                                    row['Value'] = row['Value'].decode('utf-8')
+                                except UnicodeDecodeError:
+                                    pass
                         except TypeError:
                             pass
             if isinstance(value, list) and len(value) == 1:
diff --git a/consulate/api/kv.py b/consulate/api/kv.py
index c35026d..b145719 100644
--- a/consulate/api/kv.py
+++ b/consulate/api/kv.py
@@ -336,7 +336,16 @@ def _get_modify_index(self, item, value, replace):
             index = response.body.get('ModifyIndex')
             rvalue = response.body.get('Value')
             if isinstance(rvalue, bytes):
-                rvalue = rvalue.encode('utf-8')
+                if utils.PYTHON3:
+                    try:
+                        rvalue = str(rvalue, 'utf-8')
+                    except UnicodeDecodeError:
+                        pass
+                else:
+                    try:
+                        rvalue = rvalue.encode('utf-8')
+                    except UnicodeDecodeError:
+                        pass
             if rvalue == value:
                 return None
             if not replace:
@@ -353,12 +362,15 @@ def _prepare_value(value):
         """
         if utils.is_string(value):
             if utils.PYTHON3:
-                value = value.encode('utf-8')
+                try:
+                    value = str(value, 'utf-8')
+                except UnicodeDecodeError:
+                    pass
             elif not isinstance(value, unicode):
                 try:
-                    value.decode('ascii')
+                    value.decode('utf-8')
                 except UnicodeDecodeError:
-                    value = value.decode('utf-8')
+                    pass
         return value
 
     def _set_item(self, item, value, flags=None, replace=True):