diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index cfc85520bc3..43455e0bce4 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -1184,14 +1184,12 @@ convertToLegacyPerPackageConfig PackageConfig{..} =
 --
 
 parseLegacyProjectConfigFields :: ProjectConfigImport -> [ParseUtils.Field] -> ParseResult LegacyProjectConfig
-parseLegacyProjectConfigFields pci =
+parseLegacyProjectConfigFields (ConstraintSourceProjectConfig -> constraintSrc) =
   parseFieldsAndSections
     (legacyProjectConfigFieldDescrs constraintSrc)
     legacyPackageConfigSectionDescrs
     legacyPackageConfigFGSectionDescrs
     mempty
-  where
-    constraintSrc = ConstraintSourceProjectConfig pci
 
 parseLegacyProjectConfig :: FilePath -> BS.ByteString -> ParseResult LegacyProjectConfig
 parseLegacyProjectConfig source bs = parseLegacyProjectConfigFields (ProjectConfigImport 0 source) =<< ParseUtils.readFields bs