diff --git a/src/backend/distributed/commands/table.c b/src/backend/distributed/commands/table.c
index e65f57961..c395892b5 100644
--- a/src/backend/distributed/commands/table.c
+++ b/src/backend/distributed/commands/table.c
@@ -3666,6 +3666,24 @@ ErrorIfUnsupportedAlterTableStmt(AlterTableStmt *alterTableStatement)
 
 #if PG_VERSION_NUM >= PG_VERSION_15
 			case AT_SetAccessMethod:
+			{
+				/*
+				 * If command->name == NULL, that means the user is trying to use
+				 * ALTER TABLE ... SET ACCESS METHOD DEFAULT
+				 * which we don't support currently.
+				 */
+				if (command->name == NULL)
+				{
+					ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+									errmsg(
+										"DEFAULT option in ALTER TABLE ... SET ACCESS METHOD "
+										"is currently unsupported."),
+									errhint(
+										"You can rerun the command by explicitly writing the access method name.")));
+				}
+				break;
+			}
+
 #endif
 			case AT_SetNotNull:
 			case AT_ReplicaIdentity:
diff --git a/src/test/regress/expected/pg17.out b/src/test/regress/expected/pg17.out
index 23efee4bd..fe925516b 100644
--- a/src/test/regress/expected/pg17.out
+++ b/src/test/regress/expected/pg17.out
@@ -1333,6 +1333,49 @@ SELECT b, c FROM forcetest WHERE a = 6;
 
 \pset null ''
 -- End of Testing FORCE_NOT_NULL and FORCE_NULL options
+-- Test for ALTER TABLE SET ACCESS METHOD DEFAULT
+-- Step 1: Local table setup (non-distributed)
+CREATE TABLE test_local_table (id int);
+SELECT citus_add_local_table_to_metadata('test_local_table');
+ citus_add_local_table_to_metadata
+---------------------------------------------------------------------
+
+(1 row)
+
+-- Step 2: Attempt to set access method to DEFAULT on a Citus local table (should fail)
+ALTER TABLE test_local_table SET ACCESS METHOD DEFAULT;
+ERROR:  DEFAULT option in ALTER TABLE ... SET ACCESS METHOD is currently unsupported.
+HINT:  You can rerun the command by explicitly writing the access method name.
+-- Step 3: Setup: create and distribute a table
+CREATE TABLE test_alter_access_method (id int);
+SELECT create_distributed_table('test_alter_access_method', 'id');
+ create_distributed_table
+---------------------------------------------------------------------
+
+(1 row)
+
+-- Step 4: Attempt to set access method to DEFAULT on a distributed table (should fail with your custom error)
+ALTER TABLE test_alter_access_method SET ACCESS METHOD DEFAULT;
+ERROR:  DEFAULT option in ALTER TABLE ... SET ACCESS METHOD is currently unsupported.
+HINT:  You can rerun the command by explicitly writing the access method name.
+-- Step 5: Create and distribute a partitioned table
+CREATE TABLE test_partitioned_alter (id int, val text) PARTITION BY RANGE (id);
+CREATE TABLE test_partitioned_alter_part1 PARTITION OF test_partitioned_alter FOR VALUES FROM (1) TO (100);
+SELECT create_distributed_table('test_partitioned_alter', 'id');
+ create_distributed_table
+---------------------------------------------------------------------
+
+(1 row)
+
+-- Step 6: Attempt to set access method to DEFAULT on a partitioned, distributed table (should fail)
+ALTER TABLE test_partitioned_alter SET ACCESS METHOD DEFAULT;
+ERROR:  DEFAULT option in ALTER TABLE ... SET ACCESS METHOD is currently unsupported.
+HINT:  You can rerun the command by explicitly writing the access method name.
+-- Cleanup
+DROP TABLE test_local_table CASCADE;
+DROP TABLE test_alter_access_method CASCADE;
+DROP TABLE test_partitioned_alter CASCADE;
+-- End of Test for ALTER TABLE SET ACCESS METHOD DEFAULT
 \set VERBOSITY terse
 SET client_min_messages TO WARNING;
 DROP SCHEMA pg17 CASCADE;
diff --git a/src/test/regress/sql/pg17.sql b/src/test/regress/sql/pg17.sql
index ab8528f4b..88d1a475f 100644
--- a/src/test/regress/sql/pg17.sql
+++ b/src/test/regress/sql/pg17.sql
@@ -711,6 +711,36 @@ SELECT b, c FROM forcetest WHERE a = 6;
 
 -- End of Testing FORCE_NOT_NULL and FORCE_NULL options
 
+-- Test for ALTER TABLE SET ACCESS METHOD DEFAULT
+-- Step 1: Local table setup (non-distributed)
+CREATE TABLE test_local_table (id int);
+
+SELECT citus_add_local_table_to_metadata('test_local_table');
+
+-- Step 2: Attempt to set access method to DEFAULT on a Citus local table (should fail)
+ALTER TABLE test_local_table SET ACCESS METHOD DEFAULT;
+
+-- Step 3: Setup: create and distribute a table
+CREATE TABLE test_alter_access_method (id int);
+SELECT create_distributed_table('test_alter_access_method', 'id');
+
+-- Step 4: Attempt to set access method to DEFAULT on a distributed table (should fail with your custom error)
+ALTER TABLE test_alter_access_method SET ACCESS METHOD DEFAULT;
+
+-- Step 5: Create and distribute a partitioned table
+CREATE TABLE test_partitioned_alter (id int, val text) PARTITION BY RANGE (id);
+CREATE TABLE test_partitioned_alter_part1 PARTITION OF test_partitioned_alter FOR VALUES FROM (1) TO (100);
+SELECT create_distributed_table('test_partitioned_alter', 'id');
+
+-- Step 6: Attempt to set access method to DEFAULT on a partitioned, distributed table (should fail)
+ALTER TABLE test_partitioned_alter SET ACCESS METHOD DEFAULT;
+
+-- Cleanup
+DROP TABLE test_local_table CASCADE;
+DROP TABLE test_alter_access_method CASCADE;
+DROP TABLE test_partitioned_alter CASCADE;
+-- End of Test for ALTER TABLE SET ACCESS METHOD DEFAULT
+
 \set VERBOSITY terse
 SET client_min_messages TO WARNING;
 DROP SCHEMA pg17 CASCADE;