diff --git a/CHANGELOG.md b/CHANGELOG.md
index d36a9c7c3..1788c3a2b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Fixed
 
+ - #2020, Execute deferred constraint triggers when using `Prefer: tx=rollback` - @wolfgangwalther
+
 ## [9.0.0] - 2021-11-25
 
 ### Added
diff --git a/src/PostgREST/Middleware.hs b/src/PostgREST/Middleware.hs
index fba8edddc..fb64f38ca 100644
--- a/src/PostgREST/Middleware.hs
+++ b/src/PostgREST/Middleware.hs
@@ -2,6 +2,7 @@
 Module      : PostgREST.Middleware
 Description : Sets CORS policy. Also the PostgreSQL GUCs, role, search_path and pre-request function.
 -}
+{-# LANGUAGE BlockArguments  #-}
 {-# LANGUAGE RecordWildCards #-}
 module PostgREST.Middleware
   ( runPgLocals
@@ -170,8 +171,9 @@ optionalRollback
   -> ExceptT Error SQL.Transaction Wai.Response
 optionalRollback AppConfig{..} ApiRequest{..} transaction = do
   resp <- catchError transaction $ return . errorResponseFor
-  when (shouldRollback || (configDbTxRollbackAll && not shouldCommit))
-    (lift SQL.condemn)
+  when (shouldRollback || (configDbTxRollbackAll && not shouldCommit)) $ lift do
+    SQL.sql "SET CONSTRAINTS ALL IMMEDIATE"
+    SQL.condemn
   return $ Wai.mapResponseHeaders preferenceApplied resp
   where
     shouldCommit =
diff --git a/test/Feature/RollbackSpec.hs b/test/Feature/RollbackSpec.hs
index 24bdbcd07..5ed05b9ca 100644
--- a/test/Feature/RollbackSpec.hs
+++ b/test/Feature/RollbackSpec.hs
@@ -70,6 +70,35 @@ shouldRespondToReads reqHeaders respHeaders = do
         [json|[{"id":1}]|]
         { matchHeaders = respHeaders }
 
+shouldRaiseExceptions reqHeaders respHeaders = do
+  it "raises immediate constraints" $ do
+    request methodPost "/rpc/raise_constraint"
+        reqHeaders
+        ""
+      `shouldRespondWith`
+        [json|{
+          "hint":null,
+          "details":"Key (col)=(1) already exists.",
+          "code":"23505",
+          "message":"duplicate key value violates unique constraint \"deferrable_unique_constraint_col_key\""
+        }|]
+        { matchStatus = 409
+        , matchHeaders = respHeaders }
+
+  it "raises deferred constraints" $ do
+    request methodPost "/rpc/raise_constraint"
+        reqHeaders
+        [json|{"deferred": true}|]
+      `shouldRespondWith`
+        [json|{
+          "hint":null,
+          "details":"Key (col)=(1) already exists.",
+          "code":"23505",
+          "message":"duplicate key value violates unique constraint \"deferrable_unique_constraint_col_key\""
+        }|]
+        { matchStatus = 409
+        , matchHeaders = respHeaders }
+
 shouldPersistMutations reqHeaders respHeaders = do
   it "does persist post" $ do
     request methodPost "/items"
@@ -178,28 +207,38 @@ allowed = describe "tx-allow-override = true" $ do
   describe "without Prefer tx" $ do
     preferDefault `shouldRespondToReads` withoutPreferenceApplied
     preferDefault `shouldNotPersistMutations` withoutPreferenceApplied
+    preferDefault `shouldRaiseExceptions` withoutPreferenceApplied
 
   describe "Prefer tx=commit" $ do
     preferCommit `shouldRespondToReads` withPreferenceCommitApplied
     preferCommit `shouldPersistMutations` withPreferenceCommitApplied
+    -- Exceptions are always without preference applied,
+    -- because they return before the end of the transaction.
+    preferCommit `shouldRaiseExceptions` withoutPreferenceApplied
 
   describe "Prefer tx=rollback" $ do
     preferRollback `shouldRespondToReads` withPreferenceRollbackApplied
     preferRollback `shouldNotPersistMutations` withPreferenceRollbackApplied
+    -- Exceptions are always without preference applied,
+    -- because they return before the end of the transaction.
+    preferRollback `shouldRaiseExceptions` withoutPreferenceApplied
 
 disallowed :: SpecWith ((), Application)
 disallowed = describe "tx-rollback-all = false, tx-allow-override = false" $ do
   describe "without Prefer tx" $ do
     preferDefault `shouldRespondToReads` withoutPreferenceApplied
     preferDefault `shouldPersistMutations` withoutPreferenceApplied
+    preferDefault `shouldRaiseExceptions` withoutPreferenceApplied
 
   describe "Prefer tx=commit" $ do
     preferCommit `shouldRespondToReads` withoutPreferenceApplied
     preferCommit `shouldPersistMutations` withoutPreferenceApplied
+    preferCommit `shouldRaiseExceptions` withoutPreferenceApplied
 
   describe "Prefer tx=rollback" $ do
     preferRollback `shouldRespondToReads` withoutPreferenceApplied
     preferRollback `shouldPersistMutations` withoutPreferenceApplied
+    preferRollback `shouldRaiseExceptions` withoutPreferenceApplied
 
 
 forced :: SpecWith ((), Application)
@@ -207,12 +246,15 @@ forced = describe "tx-rollback-all = true, tx-allow-override = false" $ do
   describe "without Prefer tx" $ do
     preferDefault `shouldRespondToReads` withoutPreferenceApplied
     preferDefault `shouldNotPersistMutations` withoutPreferenceApplied
+    preferDefault `shouldRaiseExceptions` withoutPreferenceApplied
 
   describe "Prefer tx=commit" $ do
     preferCommit `shouldRespondToReads` withoutPreferenceApplied
     preferCommit `shouldNotPersistMutations` withoutPreferenceApplied
+    preferCommit `shouldRaiseExceptions` withoutPreferenceApplied
 
   describe "Prefer tx=rollback" $ do
     preferRollback `shouldRespondToReads` withoutPreferenceApplied
     preferRollback `shouldNotPersistMutations` withoutPreferenceApplied
+    preferRollback `shouldRaiseExceptions` withoutPreferenceApplied
 
diff --git a/test/fixtures/privileges.sql b/test/fixtures/privileges.sql
index b103eeae3..b6899e012 100644
--- a/test/fixtures/privileges.sql
+++ b/test/fixtures/privileges.sql
@@ -25,6 +25,7 @@ GRANT ALL ON TABLE
     , complex_items
     , compound_pk
     , compound_pk_view
+    , deferrable_unique_constraint
     , empty_table
     , has_count_column
     , has_fk
diff --git a/test/fixtures/schema.sql b/test/fixtures/schema.sql
index 0c0c00273..bb92f174d 100644
--- a/test/fixtures/schema.sql
+++ b/test/fixtures/schema.sql
@@ -2448,3 +2448,17 @@ CREATE TABLE chores (
 , name text
 , done bool
 );
+
+CREATE TABLE deferrable_unique_constraint (
+  col INT UNIQUE DEFERRABLE INITIALLY IMMEDIATE
+);
+
+CREATE FUNCTION raise_constraint(deferred BOOL DEFAULT FALSE) RETURNS void
+LANGUAGE plpgsql AS $$
+BEGIN
+  IF deferred THEN
+    SET CONSTRAINTS ALL DEFERRED;
+  END IF;
+
+  INSERT INTO deferrable_unique_constraint VALUES (1), (1);
+END$$;