diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 0.1.0.39
+
+  * Restore past GHCs
+
 # 0.1.0.38
   
   * Remove dependency on `optparse-generic` as it has spurious dependencies and
diff --git a/app/Main.hs b/app/Main.hs
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -3,6 +3,7 @@
     ) where
 
 import           Control.Monad
+import           Data.Semigroup
 import qualified Data.Text.IO        as TIO
 import           Data.Version        (showVersion)
 import           Options.Applicative
diff --git a/tomlcheck.cabal b/tomlcheck.cabal
--- a/tomlcheck.cabal
+++ b/tomlcheck.cabal
@@ -1,6 +1,6 @@
 cabal-version: 1.18
 name: tomlcheck
-version: 0.1.0.38
+version: 0.1.0.39
 license: BSD3
 license-file: LICENSE
 copyright: Copyright: (c) 2017-2018 Vanessa McHale
@@ -46,7 +46,7 @@
         megaparsec >=7.0,
         text -any
 
-    if flag(development)
+    if (flag(development) && impl(ghc <8.4))
         ghc-options: -Werror
 
     if impl(ghc >=8.0)