diff --git a/library/Potoki/Core/Consume.hs b/library/Potoki/Core/Consume.hs
--- a/library/Potoki/Core/Consume.hs
+++ b/library/Potoki/Core/Consume.hs
@@ -168,7 +168,7 @@
         Just _ -> build fetchIO (succ acc)
 
 {-# INLINABLE concat #-}
-concat :: Monoid monoid => Consume monoid monoid
+concat :: (Semigroup monoid, Monoid monoid) => Consume monoid monoid
 concat =
   Consume $ \ (A.Fetch fetchIO) -> build fetchIO mempty
   where
diff --git a/potoki-core.cabal b/potoki-core.cabal
--- a/potoki-core.cabal
+++ b/potoki-core.cabal
@@ -1,7 +1,7 @@
 name:
   potoki-core
 version:
-  2.2.5.1
+  2.2.5.2
 synopsis:
   Low-level components of "potoki"
 description: