diff --git a/htest/Test/Ganeti/HTools/Cluster.hs b/htest/Test/Ganeti/HTools/Cluster.hs
index 96bd1cf52baa40f516ea5e1b4abd529ee7f1efa3..75525b4387adeab446c3be4383f0aafac7796272 100644
--- a/htest/Test/Ganeti/HTools/Cluster.hs
+++ b/htest/Test/Ganeti/HTools/Cluster.hs
@@ -37,7 +37,7 @@ import Test.Ganeti.TestHelper
 import Test.Ganeti.TestCommon
 import Test.Ganeti.TestHTools
 import Test.Ganeti.HTools.Instance ( genInstanceSmallerThanNode
-                                   , genInstanceSmallerThan )
+                                   , genInstanceMaybeBiggerThanNode )
 import Test.Ganeti.HTools.Node (genOnlineNode, genNode)
 
 import Ganeti.BasicTypes
@@ -191,10 +191,7 @@ prop_CanTieredAlloc :: Property
 prop_CanTieredAlloc =
   forAll (choose (2, 5)) $ \count ->
   forAll (genOnlineNode `suchThat` isNodeBig 4) $ \node ->
-  forAll (genInstanceSmallerThan
-            (Node.availMem  node + Types.unitMem * 2)
-            (Node.availDisk node + Types.unitDsk * 3)
-            (Node.availCpu  node + Types.unitCpu * 4)) $ \inst ->
+  forAll (genInstanceMaybeBiggerThanNode node) $ \inst ->
   let nl = makeSmallCluster node count
       il = Container.empty
       rqnodes = Instance.requiredNodes $ Instance.diskTemplate inst
diff --git a/htest/Test/Ganeti/HTools/Instance.hs b/htest/Test/Ganeti/HTools/Instance.hs
index be6adc97f30a7bb77a450b4a892bd1301470ac6b..59ef515fcbf456f5aec08d83484c3ffdb22152a3 100644
--- a/htest/Test/Ganeti/HTools/Instance.hs
+++ b/htest/Test/Ganeti/HTools/Instance.hs
@@ -29,6 +29,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 module Test.Ganeti.HTools.Instance
   ( testHTools_Instance
   , genInstanceSmallerThanNode
+  , genInstanceMaybeBiggerThanNode
   , genInstanceSmallerThan
   , Instance.Instance(..)
   ) where
@@ -66,6 +67,13 @@ genInstanceSmallerThanNode node =
                          (Node.availDisk node `div` 2)
                          (Node.availCpu node `div` 2)
 
+-- | Generates an instance possibly bigger than a node.
+genInstanceMaybeBiggerThanNode :: Node.Node -> Gen Instance.Instance
+genInstanceMaybeBiggerThanNode node =
+  genInstanceSmallerThan (Node.availMem  node + Types.unitMem * 2)
+                         (Node.availDisk node + Types.unitDsk * 3)
+                         (Node.availCpu  node + Types.unitCpu * 4)
+
 -- let's generate a random instance
 instance Arbitrary Instance.Instance where
   arbitrary = genInstanceSmallerThan maxMem maxDsk maxCpu