diff --git a/ouroboros-network-protocols/testlib/Ouroboros/Network/Protocol/LocalTxMonitor/Test.hs b/ouroboros-network-protocols/testlib/Ouroboros/Network/Protocol/LocalTxMonitor/Test.hs
index 7f4c1c6dda..bbbbcae7c4 100644
--- a/ouroboros-network-protocols/testlib/Ouroboros/Network/Protocol/LocalTxMonitor/Test.hs
+++ b/ouroboros-network-protocols/testlib/Ouroboros/Network/Protocol/LocalTxMonitor/Test.hs
@@ -242,8 +242,8 @@ instance Arbitrary MeasureName where
 
 instance Arbitrary (SizeAndCapacity Integer) where
   arbitrary = do
-    Positive s <- arbitrary
-    c <- chooseInteger (0, s)
+    Positive c <- arbitrary
+    s <- chooseInteger (0, c)
     pure $ SizeAndCapacity s c
 
 instance Arbitrary MempoolSizeAndCapacity where