diff --git a/moto/dynamodb/exceptions.py b/moto/dynamodb/exceptions.py
index 9f572764f..27d398a9c 100644
--- a/moto/dynamodb/exceptions.py
+++ b/moto/dynamodb/exceptions.py
@@ -332,3 +332,8 @@ class TransactWriteSingleOpException(MockValidationException):
 
     def __init__(self):
         super().__init__(self.there_can_be_only_one)
+
+
+class SerializationException(DynamodbException):
+    def __init__(self, msg):
+        super().__init__(error_type="SerializationException", message=msg)
diff --git a/moto/dynamodb/models/__init__.py b/moto/dynamodb/models/__init__.py
index febe9f3c5..5345ebc8d 100644
--- a/moto/dynamodb/models/__init__.py
+++ b/moto/dynamodb/models/__init__.py
@@ -33,6 +33,7 @@ from moto.dynamodb.exceptions import (
     MockValidationException,
     InvalidConversion,
     TransactWriteSingleOpException,
+    SerializationException,
 )
 from moto.dynamodb.models.utilities import bytesize
 from moto.dynamodb.models.dynamo_type import DynamoType
@@ -658,6 +659,17 @@ class Table(CloudFormationModel):
                 self._validate_item_types(value)
             elif type(value) == int and key == "N":
                 raise InvalidConversion
+            if key == "S":
+                # This scenario is usually caught by boto3, but the user can disable parameter validation
+                # Which is why we need to catch it 'server-side' as well
+                if type(value) == int:
+                    raise SerializationException(
+                        "NUMBER_VALUE cannot be converted to String"
+                    )
+                if type(value) == dict:
+                    raise SerializationException(
+                        "Start of structure or map found where not expected"
+                    )
 
     def put_item(
         self,
@@ -699,9 +711,8 @@ class Table(CloudFormationModel):
                 actual_type=range_value.type,
             )
 
-        self._validate_key_sizes(item_attrs)
-
         self._validate_item_types(item_attrs)
+        self._validate_key_sizes(item_attrs)
 
         if expected is None:
             expected = {}
diff --git a/tests/test_dynamodb/exceptions/test_dynamodb_exceptions.py b/tests/test_dynamodb/exceptions/test_dynamodb_exceptions.py
index 40767e466..069a2ba58 100644
--- a/tests/test_dynamodb/exceptions/test_dynamodb_exceptions.py
+++ b/tests/test_dynamodb/exceptions/test_dynamodb_exceptions.py
@@ -870,3 +870,29 @@ def test_update_primary_key():
     table.get_item(Key={"pk": "testchangepk"})["Item"].should.equal(
         {"pk": "testchangepk"}
     )
+
+
+@mock_dynamodb
+def test_put_item__string_as_integer_value():
+    if settings.TEST_SERVER_MODE:
+        raise SkipTest("Unable to mock a session with Config in ServerMode")
+    session = botocore.session.Session()
+    config = botocore.client.Config(parameter_validation=False)
+    client = session.create_client("dynamodb", region_name="us-east-1", config=config)
+    client.create_table(
+        TableName="without_sk",
+        KeySchema=[{"AttributeName": "pk", "KeyType": "HASH"}],
+        AttributeDefinitions=[{"AttributeName": "pk", "AttributeType": "S"}],
+        ProvisionedThroughput={"ReadCapacityUnits": 10, "WriteCapacityUnits": 10},
+    )
+    with pytest.raises(ClientError) as exc:
+        client.put_item(TableName="without_sk", Item={"pk": {"S": 123}})
+    err = exc.value.response["Error"]
+    err["Code"].should.equal("SerializationException")
+    err["Message"].should.equal("NUMBER_VALUE cannot be converted to String")
+
+    with pytest.raises(ClientError) as exc:
+        client.put_item(TableName="without_sk", Item={"pk": {"S": {"S": "asdf"}}})
+    err = exc.value.response["Error"]
+    err["Code"].should.equal("SerializationException")
+    err["Message"].should.equal("Start of structure or map found where not expected")