diff --git a/changelog.d/0-release-notes/WPB-27953-make-scim-error-responses-comply-with-rfc7644 b/changelog.d/0-release-notes/WPB-27953-make-scim-error-responses-comply-with-rfc7644
new file mode 100644
index 00000000000..d769a62ddfb
--- /dev/null
+++ b/changelog.d/0-release-notes/WPB-27953-make-scim-error-responses-comply-with-rfc7644
@@ -0,0 +1,22 @@
+Make SCIM error responses comply with RFC7644.  Any code that processes SCIM error responses must be changed to follow the standard, instead of the previous Wire implementation.
+
+Previous schema (incompatible with RFC):
+
+```
+{
+  "code": 400,
+  "label": "scim-error",
+  "message": "{\"detail\":\"[...]\",\"schemas\":[\"urn:ietf:params:scim:api:messages:2.0:Error\"],\"scimType\":\"invalidValue\",\"status\":\"400\"}"
+}
+```
+
+New schema (RFC-compliant):
+
+```
+{
+  "schemas": ["urn:ietf:params:scim:api:messages:2.0:Error"],
+  "status": "400"
+  "scimType": "invalidValue",
+  "detail": "[...]",
+}
+```
diff --git a/changelog.d/1-api-changes/WPB-27953-make-scim-error-responses-comply-with-rfc7644 b/changelog.d/1-api-changes/WPB-27953-make-scim-error-responses-comply-with-rfc7644
new file mode 100644
index 00000000000..f03aeea44f6
--- /dev/null
+++ b/changelog.d/1-api-changes/WPB-27953-make-scim-error-responses-comply-with-rfc7644
@@ -0,0 +1 @@
+Make scim error responses comply with RFC7644.
diff --git a/services/spar/spar.cabal b/services/spar/spar.cabal
index 8bd4d03aac8..962388000ed 100644
--- a/services/spar/spar.cabal
+++ b/services/spar/spar.cabal
@@ -530,6 +530,7 @@ test-suite spec
     Paths_spar
     Test.Spar.APISpec
     Test.Spar.DataSpec
+    Test.Spar.ErrorSpec
     Test.Spar.Intra.BrigSpec
     Test.Spar.Roundtrip.ByteString
     Test.Spar.Saml.IdPSpec
diff --git a/services/spar/src/Spar/Error.hs b/services/spar/src/Spar/Error.hs
index f15cb5dfad0..a2cd61d9f73 100644
--- a/services/spar/src/Spar/Error.hs
+++ b/services/spar/src/Spar/Error.hs
@@ -135,7 +135,13 @@ sparToServerErrorWithLogging logger err = do
   pure errServant
 
 sparToServerError :: SparError -> ServerError
-sparToServerError = httpErrorToServerError . renderSparError
+-- SCIM errors have their own response format (RFC 7644, section 3.12): the body
+-- must be the bare SCIM error object.  Going through 'renderSparError' /
+-- 'httpErrorToServerError' would instead nest it into a wire-server 'Wai.Error'
+-- ('{"code":..,"label":"scim-error","message":<scim error as string>}'), so we
+-- render it directly here.
+sparToServerError (SAML.CustomError (SparScimError err)) = Scim.scimToServerError err
+sparToServerError err = httpErrorToServerError (renderSparError err)
 
 waiToServant :: Wai.Error -> ServerError
 waiToServant waierr =
diff --git a/services/spar/test/Test/Spar/ErrorSpec.hs b/services/spar/test/Test/Spar/ErrorSpec.hs
new file mode 100644
index 00000000000..1f0b697ab53
--- /dev/null
+++ b/services/spar/test/Test/Spar/ErrorSpec.hs
@@ -0,0 +1,55 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+-- This file is part of the Wire Server implementation.
+--
+-- Copyright (C) 2025 Wire Swiss GmbH <opensource@wire.com>
+--
+-- This program is free software: you can redistribute it and/or modify it under
+-- the terms of the GNU Affero General Public License as published by the Free
+-- Software Foundation, either version 3 of the License, or (at your option) any
+-- later version.
+--
+-- This program is distributed in the hope that it will be useful, but WITHOUT
+-- ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+-- FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+-- details.
+--
+-- You should have received a copy of the GNU Affero General Public License along
+-- with this program. If not, see <https://www.gnu.org/licenses/>.
+
+module Test.Spar.ErrorSpec where
+
+import Data.Aeson (eitherDecode')
+import Data.Aeson.QQ (aesonQQ)
+import Imports
+import qualified SAML2.WebSSO as SAML
+import Servant (ServerError (..))
+import Spar.Error
+import Test.Hspec
+import qualified Web.Scim.Schema.Error as Scim
+
+spec :: Spec
+spec = describe "sparToServerError" $ do
+  -- RFC 7644 section 3.12 requires that the response body of a SCIM error *is*
+  -- the SCIM error object, not a wire-server 'Wai.Error' with the SCIM error
+  -- object nested (double-encoded) into its 'message' field.
+  it "renders a SCIM error as the bare RFC 7644 error object" $ do
+    let scimErr =
+          Scim.badRequest
+            Scim.InvalidValue
+            (Just "Could not process externalId.")
+        serverErr = sparToServerError (SAML.CustomError (SparScimError scimErr))
+    eitherDecode' (errBody serverErr)
+      `shouldBe` Right
+        [aesonQQ|
+                  {
+                    "detail": "Could not process externalId.",
+                    "schemas": [
+                      "urn:ietf:params:scim:api:messages:2.0:Error"
+                    ],
+                    "scimType": "invalidValue",
+                    "status": "400"
+                  }|]
+    errHTTPCode serverErr `shouldBe` 400
+    lookup "Content-Type" (errHeaders serverErr)
+      `shouldBe` Just "application/scim+json;charset=utf-8"