diff --git a/builder/haddock-builder.nix b/builder/haddock-builder.nix
index 24f56cbf0..ae6a85325 100644
--- a/builder/haddock-builder.nix
+++ b/builder/haddock-builder.nix
@@ -109,6 +109,12 @@ let
 
       # If we don't have any source files, no need to run haddock
       [[ -n $(find . -name "*.hs" -o -name "*.lhs") ]] && {
+      # Run any preprocessor in the custom build step
+      $SETUP_HS build \
+        "--with-ghc=false" \
+        ${lib.optionalString (haskellLib.isTest componentId) "--tests"} \
+        ${lib.concatStringsSep " " setupHaddockFlags} || true
+
       $SETUP_HS haddock \
         "--html" \
         ${lib.optionalString (haskellLib.isTest componentId) "--tests"} \
diff --git a/ci.nix b/ci.nix
index e07482ba5..cbef43e89 100644
--- a/ci.nix
+++ b/ci.nix
@@ -66,10 +66,10 @@
       # from here (so that is no longer cached) also remove ./materialized/ghcXXX.
       # Update supported-ghc-versions.md to reflect any changes made here.
       nixpkgs.lib.optionalAttrs (builtins.elem nixpkgsName ["R2411" "R2505"]) {
-        ghc96 = true;
-        ghc98 = true;
-        ghc910 = true;
-        ghc912 = true;
+        ghc96 = false;
+        ghc98 = false;
+        ghc910 = false;
+        ghc912 = false;
       } // nixpkgs.lib.optionalAttrs (nixpkgsName == "unstable") {
         ghc96 = true;
         ghc98 = true;