diff --git a/cubes-mongo/browser.py b/cubes-mongo/browser.py
index 202316b..42d4ebd 100644
--- a/cubes-mongo/browser.py
+++ b/cubes-mongo/browser.py
@@ -403,7 +403,10 @@ def _date_transform(item, date_field):
                 group = phys.group
             elif function:
                 group_applicator = function["group_by"]
-                group = group_applicator(escape_level(agg.measure.ref()))
+		if agg.measure:
+			group = group_applicator(escape_level(agg.measure))
+		else:
+			group = group_applicator(escape_level(agg.ref()))
             else:
                 raise ModelError("Neither function or mapping group specified "
                                  "for aggregate '%s' in cube '%s'"
@@ -420,10 +423,11 @@ def _date_transform(item, date_field):
             pipeline = []
 
         pipeline.append({ "$match": query_obj })
-        if fields_obj:
-            pipeline.append({ "$project": fields_obj })
         pipeline.append({ "$group": group_obj })
 
+	if fields_obj:
+            pipeline.append({ "$project": fields_obj })
+
         if not timezone_shift_processing:
             if order:
                 obj = {
diff --git a/cubes-mongo/functions.py b/cubes-mongo/functions.py
index bcf6a28..2179d46 100644
--- a/cubes-mongo/functions.py
+++ b/cubes-mongo/functions.py
@@ -32,7 +32,19 @@
     'custom': {
         'group_by' : (lambda field: { '$sum': 1 }),
         'aggregate_fn': len
-    }
+    },
+    'min': {
+	'group_by': (lambda field: { '$min': "$%s" % field }),
+        'aggregate_fn': min,
+    },
+    'max': {
+        'group_by': (lambda field: { '$max': "$%s" % field }),
+        'aggregate_fn': max,
+    },
+    'avg': {
+        'group_by': (lambda field: { '$avg': "$%s" % field }),
+        'aggregate_fn': sum,
+    },
 }