diff --git a/edb/pgsql/resolver/expr.py b/edb/pgsql/resolver/expr.py
index b6f01d7edd5..619df240ca7 100644
--- a/edb/pgsql/resolver/expr.py
+++ b/edb/pgsql/resolver/expr.py
@@ -632,6 +632,8 @@ def resolve_LockingClause(
     'jsonb_object_agg_unique',
     'json_object_agg_unique_strict',
     'jsonb_object_agg_unique_strict',
+    'date_part',
+    'date_trunc',
 }
 
 
diff --git a/edb/server/protocol/pg_ext.pyx b/edb/server/protocol/pg_ext.pyx
index 343bc1b6b10..055c93ae3f7 100644
--- a/edb/server/protocol/pg_ext.pyx
+++ b/edb/server/protocol/pg_ext.pyx
@@ -1932,12 +1932,15 @@ cdef bytes remap_arguments(
         if arg_offset_external < offset:
             buf.write_bytes(data[arg_offset_external:offset])
 
-        # write non-external args
-        extracted_consts = list(source.variables().values())
-        for (e, param) in enumerate(params[param_count_external:]):
-            if isinstance(param, dbstate.SQLParamExtractedConst):
-                buf.write_len_prefixed_bytes(extracted_consts[e])
-            elif isinstance(param, dbstate.SQLParamGlobal):
+        # Write extracted consts from extra_blobs. The blob already contains
+        # all len-prefixed values in param order (matching args_ser.pyx pattern).
+        extra_blobs = source.extra_blobs()
+        if extra_blobs:
+            buf.write_bytes(extra_blobs[0])
+
+        # Write globals
+        for param in params[param_count_external:]:
+            if isinstance(param, dbstate.SQLParamGlobal):
                 name = param.global_name
                 if param.is_permission:
                     buf.write_int32(1)
diff --git a/tests/test_sql_dml.py b/tests/test_sql_dml.py
index eca12db5993..a5d26028bb0 100644
--- a/tests/test_sql_dml.py
+++ b/tests/test_sql_dml.py
@@ -2545,3 +2545,28 @@ async def test_sql_dml_03(self):
             '''SELECT COUNT(*) FROM "Child.tags"'''
         )
         self.assertEqual(res, [[1]])
+
+    async def test_sql_dml_date_trunc_group_by(self):
+        # Regression test for DATE_TRUNC with GROUP BY
+        await self.scon.execute(
+            '''
+            INSERT INTO "Post" (title, created_at) VALUES
+            ('Post 1', '2024-01-15 10:00:00+00'),
+            ('Post 2', '2024-01-20 15:30:00+00'),
+            ('Post 3', '2024-02-10 09:00:00+00')
+            '''
+        )
+
+        res = await self.squery_values(
+            '''
+            SELECT
+                DATE_TRUNC('month', p.created_at) as log_date,
+                COUNT(*) as log_count
+            FROM "Post" p
+            GROUP BY DATE_TRUNC('month', p.created_at)
+            ORDER BY log_date
+            '''
+        )
+        self.assertEqual(len(res), 2)
+        self.assertEqual(res[0][1], 2)  # January count
+        self.assertEqual(res[1][1], 1)  # February count