diff --git a/moto/iot/models.py b/moto/iot/models.py
index 713d02d27..56a852dbe 100644
--- a/moto/iot/models.py
+++ b/moto/iot/models.py
@@ -1301,14 +1301,17 @@ class IoTBackend(BaseBackend):
         if attribute_payload is not None and "attributes" in attribute_payload:
             do_merge = attribute_payload.get("merge", False)
             attributes = attribute_payload["attributes"]
-            if not do_merge:
-                thing_group.thing_group_properties["attributePayload"][
-                    "attributes"
-                ] = attributes
-            else:
-                thing_group.thing_group_properties["attributePayload"][
-                    "attributes"
-                ].update(attributes)
+            if attributes:
+                # might not exist yet, for example when the thing group was created without attributes
+                current_attribute_payload = (
+                    thing_group.thing_group_properties.setdefault(
+                        "attributePayload", {"attributes": {}}
+                    )
+                )
+                if not do_merge:
+                    current_attribute_payload["attributes"] = attributes
+                else:
+                    current_attribute_payload["attributes"].update(attributes)
         elif attribute_payload is not None and "attributes" not in attribute_payload:
             thing_group.attributes = {}
         if "thingGroupDescription" in thing_group_properties:
diff --git a/tests/test_iot/test_iot_thing_groups.py b/tests/test_iot/test_iot_thing_groups.py
index d5b08daaa..fca1d23d6 100644
--- a/tests/test_iot/test_iot_thing_groups.py
+++ b/tests/test_iot/test_iot_thing_groups.py
@@ -615,3 +615,73 @@ def test_thing_group_updates_description():
     thing_group.should.have.key("thingGroupProperties").which.should.have.key(
         "thingGroupDescription"
     ).which.should.equal(new_description)
+
+
+@mock_iot
+def test_thing_group_update_with_no_previous_attributes_no_merge():
+    client = boto3.client("iot", region_name="ap-northeast-1")
+    name = "my-group-name"
+    client.create_thing_group(thingGroupName=name)
+
+    client.update_thing_group(
+        thingGroupName=name,
+        thingGroupProperties={
+            "attributePayload": {
+                "attributes": {
+                    "key1": "val01",
+                },
+                "merge": False,
+            }
+        },
+    )
+
+    updated_thing_group = client.describe_thing_group(thingGroupName=name)
+    updated_thing_group.should.have.key("thingGroupProperties").which.should.have.key(
+        "attributePayload"
+    ).which.should.have.key("attributes").which.should.equal({"key1": "val01"})
+
+
+@mock_iot
+def test_thing_group_update_with_no_previous_attributes_with_merge():
+    client = boto3.client("iot", region_name="ap-northeast-1")
+    name = "my-group-name"
+    client.create_thing_group(thingGroupName=name)
+
+    client.update_thing_group(
+        thingGroupName=name,
+        thingGroupProperties={
+            "attributePayload": {
+                "attributes": {
+                    "key1": "val01",
+                },
+                "merge": True,
+            }
+        },
+    )
+
+    updated_thing_group = client.describe_thing_group(thingGroupName=name)
+    updated_thing_group.should.have.key("thingGroupProperties").which.should.have.key(
+        "attributePayload"
+    ).which.should.have.key("attributes").which.should.equal({"key1": "val01"})
+
+
+@mock_iot
+def test_thing_group_updated_with_empty_attributes_no_merge_no_attributes_added():
+    client = boto3.client("iot", region_name="ap-northeast-1")
+    name = "my-group-name"
+    client.create_thing_group(thingGroupName=name)
+
+    client.update_thing_group(
+        thingGroupName=name,
+        thingGroupProperties={
+            "attributePayload": {
+                "attributes": {},
+                "merge": False,
+            }
+        },
+    )
+
+    updated_thing_group = client.describe_thing_group(thingGroupName=name)
+    updated_thing_group.should.have.key(
+        "thingGroupProperties"
+    ).which.should_not.have.key("attributePayload")