diff --git a/ckanext/harvest/plugin/__init__.py b/ckanext/harvest/plugin/__init__.py
index d412fd22..3c22c6a8 100644
--- a/ckanext/harvest/plugin/__init__.py
+++ b/ckanext/harvest/plugin/__init__.py
@@ -2,6 +2,7 @@
 
 import os
 import json
+import six
 from logging import getLogger
 
 from six import string_types
@@ -110,7 +111,7 @@ def before_dataset_search(self, search_params):
 
         fq = search_params.get("fq", "")
         if "dataset_type:harvest" not in fq:
-            fq = "{0} -dataset_type:harvest".format(search_params.get("fq", ""))
+            fq = "{0} -dataset_type:harvest".format(fq.encode('utf8') if six.PY2 else fq)
             search_params.update({"fq": fq})
 
         return search_params