diff --git a/src/runtime/haskell/PGF2/Transactions.hsc b/src/runtime/haskell/PGF2/Transactions.hsc
index fce691436..a37599be1 100644
--- a/src/runtime/haskell/PGF2/Transactions.hsc
+++ b/src/runtime/haskell/PGF2/Transactions.hsc
@@ -164,7 +164,8 @@ createConcrete name (Transaction f) = Transaction $ \c_db c_abstr c_revision c_e
 alterConcrete :: ConcName -> Transaction Concr () -> Transaction PGF ()
 alterConcrete name (Transaction f) = Transaction $ \c_db c_abstr c_revision c_exn ->
   withText name $ \c_name -> do
-    c_concr_revision <- pgf_clone_concrete c_db c_revision c_name c_exn
+  bracket (pgf_clone_concrete c_db c_revision c_name c_exn)
+          (pgf_free_concr_revision_ c_db) $ \c_concr_revision ->
     f c_db c_abstr c_concr_revision c_exn
 
 dropConcrete :: ConcName -> Transaction PGF ()