diff --git a/pywikibot/data/api.py b/pywikibot/data/api.py
index c305dda8..cf7df7a0 100644
--- a/pywikibot/data/api.py
+++ b/pywikibot/data/api.py
@@ -555,6 +555,8 @@ class ParamInfo(Container):
             # query modules can be prefixed with 'query+'
             self._init()
 
+        modules = self._modules_to_set(modules)
+
         if self._action_modules:
             # The query module may be added before the action modules have been
             if 'query' in self._modules:
@@ -735,12 +737,21 @@ class ParamInfo(Container):
                 assert param['name'] == 'generator' and \
                     submodules >= set(param['type'])
 
-    def _normalize_modules(self, modules):
-        """Add query+ to any query module name not also in action modules."""
-        # Users will supply the wrong type, and expect it to work.
+    @staticmethod
+    def _modules_to_set(modules):
+        """Return modules as a set.
+
+        @type modules: Iterable, basestring, set
+        @rtype: set
+        """
+        if isinstance(modules, set):
+            return modules
         if isinstance(modules, basestring):
-            modules = set(modules.split('|'))
+            return set(modules.split('|'))
+        return set(modules)
 
+    def _normalize_modules(self, modules):
+        """Add query+ to any query module name not also in action modules."""
         assert(self._action_modules)
 
         return {'query+' + mod
@@ -759,7 +770,7 @@ class ParamInfo(Container):
         @rtype: set
         """
         self._init()
-        return self._normalize_modules(modules)
+        return self._normalize_modules(self._modules_to_set(modules))
 
     @classmethod
     def normalize_paraminfo(cls, data):