diff --git a/hw-prim.cabal b/hw-prim.cabal
--- a/hw-prim.cabal
+++ b/hw-prim.cabal
@@ -1,7 +1,7 @@
 cabal-version:  2.2
 
 name:           hw-prim
-version:        0.6.2.32
+version:        0.6.2.33
 synopsis:       Primitive functions and data types
 description:    Primitive functions and data types.
 category:       Data
diff --git a/src/HaskellWorks/Data/Vector/Storable.hs b/src/HaskellWorks/Data/Vector/Storable.hs
--- a/src/HaskellWorks/Data/Vector/Storable.hs
+++ b/src/HaskellWorks/Data/Vector/Storable.hs
@@ -109,9 +109,8 @@
 construct64UnzipN nBytes xs = (DVS.unsafeCast ibv, DVS.unsafeCast bpv)
   where [ibv, bpv] = DVS.createT $ do
           let nW64s     = (nBytes + 7) `div` 8
-          let capacity  = nW64s * 8
-          ibmv <- DVSM.new capacity
-          bpmv <- DVSM.new capacity
+          ibmv <- DVSM.new nW64s
+          bpmv <- DVSM.new nW64s
           (ibmvRemaining, bpmvRemaining) <- go ibmv bpmv xs
           return
             [ DVSM.take (((DVSM.length ibmv - ibmvRemaining) `div` 8) * 8) ibmv