diff --git a/src/common/dataforms.py b/src/common/dataforms.py
index e8ba22588..ffb15926d 100644
--- a/src/common/dataforms.py
+++ b/src/common/dataforms.py
@@ -146,7 +146,7 @@ class DataField(ExtendedNode):
             return t
 
         def fset(self, value):
-            assert isinstance(value, basestring)
+            assert isinstance(value, str)
             self.setAttr('type', value)
 
         return locals()
@@ -160,7 +160,7 @@ class DataField(ExtendedNode):
             return self.getAttr('var')
 
         def fset(self, value):
-            assert isinstance(value, basestring)
+            assert isinstance(value, str)
             self.setAttr('var', value)
 
         def fdel(self):
@@ -180,7 +180,7 @@ class DataField(ExtendedNode):
             return l
 
         def fset(self, value):
-            assert isinstance(value, basestring)
+            assert isinstance(value, str)
             self.setAttr('label', value)
 
         def fdel(self):
@@ -198,7 +198,7 @@ class DataField(ExtendedNode):
             return self.getTagData('desc') or ''
 
         def fset(self, value):
-            assert isinstance(value, basestring)
+            assert isinstance(value, str)
             if value == '':
                 fdel(self)
             else:
@@ -351,7 +351,7 @@ class StringField(DataField):
             return self.getTagData('value') or ''
 
         def fset(self, value):
-            assert isinstance(value, basestring)
+            assert isinstance(value, str)
             if value == '' and not self.required:
                 return fdel(self)
             self.setTagData('value', value)
diff --git a/src/groups.py b/src/groups.py
index 4e190cdf8..3ead0aa92 100644
--- a/src/groups.py
+++ b/src/groups.py
@@ -31,8 +31,8 @@ class GroupsPostWindow:
         Open new 'create post' window to create message for groupid on servicejid
         service
         """
-        assert isinstance(servicejid, basestring)
-        assert isinstance(groupid, basestring)
+        assert isinstance(servicejid, str)
+        assert isinstance(groupid, str)
 
         self.account = account
         self.servicejid = servicejid
diff --git a/src/gtkgui_helpers.py b/src/gtkgui_helpers.py
index 0a85dc9c8..66ed11577 100644
--- a/src/gtkgui_helpers.py
+++ b/src/gtkgui_helpers.py
@@ -315,7 +315,7 @@ class HashDigest:
         sa, sd = self.algo, self.digest
         if isinstance(other, self.__class__):
             oa, od = other.algo, other.digest
-        elif isinstance(other, basestring):
+        elif isinstance(other, str):
             sa, oa, od = None, None, self.cleanID(other)
         elif isinstance(other, tuple) and len(other) == 2:
             oa, od = self.cleanID(other[0]), self.cleanID(other[1])