diff --git a/bump_pydantic/codemods/validator.py b/bump_pydantic/codemods/validator.py
index a2fe7fc..6709ce5 100644
--- a/bump_pydantic/codemods/validator.py
+++ b/bump_pydantic/codemods/validator.py
@@ -140,6 +140,13 @@ def leave_validator_func(self, original_node: cst.FunctionDef, updated_node: cst
             self._should_add_comment = False
             return updated_node
 
+        # Check if a classmethod decorator already exists
+        if any(
+            m.matches(decorator, m.Decorator(decorator=m.Name("classmethod"))) for decorator in updated_node.decorators
+        ):
+            return updated_node  # If it already exists, return the node as is
+
+        # If it doesn't exist, add the classmethod decorator
         classmethod_decorator = cst.Decorator(decorator=cst.Name("classmethod"))
         return updated_node.with_changes(decorators=[*updated_node.decorators, classmethod_decorator])
 
diff --git a/tests/integration/cases/replace_validator.py b/tests/integration/cases/replace_validator.py
index 82009b5..dc5616a 100644
--- a/tests/integration/cases/replace_validator.py
+++ b/tests/integration/cases/replace_validator.py
@@ -45,6 +45,51 @@
             ],
         ),
     ),
+    Case(
+        name="Replace validator with existing classmethod decorator",
+        source=File(
+            "replace_validator_existing_classmethod.py",
+            content=[
+                "from pydantic import BaseModel, validator, root_validator",
+                "",
+                "",
+                "class A(BaseModel):",
+                "    a: int",
+                "    b: str",
+                "",
+                "    @validator('a')",
+                "    @classmethod",
+                "    def validate_a(cls, v):",
+                "        return v + 1",
+                "",
+                "    @root_validator()",
+                "    @classmethod",
+                "    def validate_b(cls, values):",
+                "        return values",
+            ],
+        ),
+        expected=File(
+            "replace_validator_existing_classmethod.py",
+            content=[
+                "from pydantic import field_validator, model_validator, BaseModel",
+                "",
+                "",
+                "class A(BaseModel):",
+                "    a: int",
+                "    b: str",
+                "",
+                "    @field_validator('a')",
+                "    @classmethod",
+                "    def validate_a(cls, v):",
+                "        return v + 1",
+                "",
+                "    @model_validator()",
+                "    @classmethod",
+                "    def validate_b(cls, values):",
+                "        return values",
+            ],
+        ),
+    ),
     Case(
         name="Replace validator with pre=True",
         source=File(
diff --git a/tests/unit/test_validator.py b/tests/unit/test_validator.py
index 2a8e289..f6d9501 100644
--- a/tests/unit/test_validator.py
+++ b/tests/unit/test_validator.py
@@ -278,6 +278,51 @@ def _string_validator(cls, v: t.Any) -> t.Optional[str]:
         """
         self.assertCodemod(before, after)
 
+    def test_replace_validator_existing_classmethod_decorator(self) -> None:
+        before = """
+        from pydantic import validator
+
+
+        class Potato(BaseModel):
+            name: str
+            dialect: str
+
+            @root_validator(pre=True, allow_reuse=True)
+            @classmethod
+            def _normalize_fields(cls, values: t.Dict[str, t.Any]) -> t.Dict[str, t.Any]:
+                if "gateways" not in values and "gateway" in values:
+                    values["gateways"] = values.pop("gateway")
+
+            @validator("name", "dialect", pre=False)
+            @classmethod
+            def _string_validator(cls, v: t.Any) -> t.Optional[str]:
+                if isinstance(v, exp.Expression):
+                    return v.name.lower()
+                return str(v).lower() if v is not None else None
+        """
+        after = """
+        from pydantic import field_validator, model_validator
+
+
+        class Potato(BaseModel):
+            name: str
+            dialect: str
+
+            @model_validator(mode="before")
+            @classmethod
+            def _normalize_fields(cls, values: t.Dict[str, t.Any]) -> t.Dict[str, t.Any]:
+                if "gateways" not in values and "gateway" in values:
+                    values["gateways"] = values.pop("gateway")
+
+            @field_validator("name", "dialect")
+            @classmethod
+            def _string_validator(cls, v: t.Any) -> t.Optional[str]:
+                if isinstance(v, exp.Expression):
+                    return v.name.lower()
+                return str(v).lower() if v is not None else None
+        """
+        self.assertCodemod(before, after)
+
     @pytest.mark.xfail(reason="Not implemented yet")
     def test_import_pydantic(self) -> None:
         before = """