diff --git a/bytestring-strict-builder.cabal b/bytestring-strict-builder.cabal
--- a/bytestring-strict-builder.cabal
+++ b/bytestring-strict-builder.cabal
@@ -1,7 +1,7 @@
 name:
   bytestring-strict-builder
 version:
-  0.4.5.2
+  0.4.5.3
 category:
   Text, ByteString, Builders, Serialization
 synopsis:
@@ -100,5 +100,5 @@
     Haskell2010
   build-depends:
     bytestring-strict-builder,
-    criterion >= 1.1 && < 1.5,
+    criterion >= 1.1 && < 1.6,
     rerebase == 1.*
diff --git a/library/ByteString/StrictBuilder.hs b/library/ByteString/StrictBuilder.hs
--- a/library/ByteString/StrictBuilder.hs
+++ b/library/ByteString/StrictBuilder.hs
@@ -46,7 +46,7 @@
     Builder size population
     where
       size =
-        getSum (foldMap (\(Builder x _) -> Sum x) builders)
+        foldl' (\acc (Builder x _) -> acc + x) 0 builders
       population =
         foldMap (\(Builder _ x) -> x) builders