diff --git a/pkgs/development/haskell-modules/configuration-common.nix b/pkgs/development/haskell-modules/configuration-common.nix
index e9f2c10f3617..fdadfda14386 100644
--- a/pkgs/development/haskell-modules/configuration-common.nix
+++ b/pkgs/development/haskell-modules/configuration-common.nix
@@ -2120,6 +2120,9 @@ with haskellLib;
     doJailbreak
   ];
 
+  # 2026-06-10: pin validation to < 1.2 due to breaking API changes affecting geojson
+  validation = super.validation_1_1_5;
+
   # too strict bounds on extra < 1.8
   # https://github.com/georgefst/svgone/pull/3
   svgone = doJailbreak super.svgone;
diff --git a/pkgs/development/haskell-modules/configuration-hackage2nix/main.yaml b/pkgs/development/haskell-modules/configuration-hackage2nix/main.yaml
index 382ccdca7b4b..4dd8652f5b3f 100644
--- a/pkgs/development/haskell-modules/configuration-hackage2nix/main.yaml
+++ b/pkgs/development/haskell-modules/configuration-hackage2nix/main.yaml
@@ -129,6 +129,7 @@ extra-packages:
   - tar == 0.6.3.0                      # 2025-08-17: last version to not require file-io and directory-ospath-streaming (for GHC < 9.6)
   - text-builder < 1                    # 2025-08-27: Needed for building postgrest
   - text-builder-dev < 0.4              # 2025-08-27: Needed for building postgrest
+  - validation == 1.1.5                 # 2026-06-10: Needed for building geojson 4.1
 # keep-sorted end
 
 # keep-sorted start skip_lines=1 case=no
diff --git a/pkgs/development/haskell-modules/hackage-packages.nix b/pkgs/development/haskell-modules/hackage-packages.nix
index fe312aa42c02..e35fb83efd2e 100644
--- a/pkgs/development/haskell-modules/hackage-packages.nix
+++ b/pkgs/development/haskell-modules/hackage-packages.nix
@@ -732304,6 +732304,47 @@ self: {
     }
   ) { };
 
+  validation_1_1_5 = callPackage (
+    {
+      mkDerivation,
+      assoc,
+      base,
+      bifunctors,
+      deepseq,
+      hedgehog,
+      HUnit,
+      lens,
+      selective,
+      semigroupoids,
+      semigroups,
+    }:
+    mkDerivation {
+      pname = "validation";
+      version = "1.1.5";
+      sha256 = "1xi4iynz82743zv5pyjd779y8qf1nzp5glmci5cxwndic6kxkp8k";
+      libraryHaskellDepends = [
+        assoc
+        base
+        bifunctors
+        deepseq
+        lens
+        selective
+        semigroupoids
+        semigroups
+      ];
+      testHaskellDepends = [
+        base
+        hedgehog
+        HUnit
+        lens
+        semigroups
+      ];
+      description = "A data-type like Either but with an accumulating Applicative";
+      license = lib.licenses.bsd3;
+      hydraPlatforms = lib.platforms.none;
+    }
+  ) { };
+
   validation = callPackage (
     {
       mkDerivation,