diff --git a/addons/purchase/report/purchase_report.py b/addons/purchase/report/purchase_report.py
index 6b68cecf1a5..c91920a0d86 100644
--- a/addons/purchase/report/purchase_report.py
+++ b/addons/purchase/report/purchase_report.py
@@ -93,7 +93,7 @@ class purchase_report(osv.osv):
                     l.product_id,
                     t.categ_id as category_id,
                     (case when u.uom_type not in ('reference') then
-                            (select id from product_uom where uom_type='reference' and category_id = 1)
+                            (select id from product_uom where uom_type='reference' and category_id = 1 LIMIT 1)
                     else
                         u.id
                     end) as product_uom,
diff --git a/addons/sale/report/sale_report.py b/addons/sale/report/sale_report.py
index aaaec228d7b..ed457835fb6 100644
--- a/addons/sale/report/sale_report.py
+++ b/addons/sale/report/sale_report.py
@@ -91,7 +91,7 @@ class sale_report(osv.osv):
                     select l.id as id,
                         l.product_id as product_id,
                         (case when u.uom_type not in ('reference') then
-                            (select name from product_uom where uom_type='reference' and category_id=u.category_id)
+                            (select name from product_uom where uom_type='reference' and category_id=u.category_id LIMIT 1)
                         else
                             u.name
                         end) as uom_name,