diff --git a/vizro-core/schemas/0.2.0.dev0.json b/vizro-core/schemas/0.2.0.dev0.json
index 63f4037f8..cfa0886da 100644
--- a/vizro-core/schemas/0.2.0.dev0.json
+++ b/vizro-core/schemas/0.2.0.dev0.json
@@ -1268,7 +1268,7 @@
     },
     "RangeSlider": {
       "additionalProperties": false,
-      "description": "Numeric multi-option selector `RangeSlider`.\n\nCan be provided to [`Filter`][vizro.models.Filter] or\n[`Parameter`][vizro.models.Parameter]. Based on the underlying\n[`dcc.RangeSlider`](https://dash.plotly.com/dash-core-components/rangeslider).\n\nArgs:\n    type (Literal[\"range_slider\"]): Defaults to `\"range_slider\"`.\n    min (Optional[float]): Start value for slider. Defaults to `None`.\n    max (Optional[float]): End value for slider. Defaults to `None`.\n    step (Optional[float]): Step-size for marks on slider. Defaults to `None`.\n    marks (Optional[dict[float, str]]): Marks to be displayed on slider. Defaults to `{}`.\n    value (Optional[list[float]]): Default start and end value for slider. Must be 2 items. Defaults to `None`.\n    title (str): Title to be displayed. Defaults to `\"\"`.\n    actions (list[Action]): See [`Action`][vizro.models.Action]. Defaults to `[]`.",
+      "description": "Numeric multi-option selector `RangeSlider`.\n\nCan be provided to [`Filter`][vizro.models.Filter] or\n[`Parameter`][vizro.models.Parameter]. Based on the underlying\n[`dcc.RangeSlider`](https://dash.plotly.com/dash-core-components/rangeslider).\n\nArgs:\n    type (Literal[\"range_slider\"]): Defaults to `\"range_slider\"`.\n    min (Optional[float]): Start value for slider. Defaults to `None`.\n    max (Optional[float]): End value for slider. Defaults to `None`.\n    step (Optional[float]): Step-size for marks on slider. Defaults to `None`.\n    marks (Optional[dict[Union[float, int], str]]): Marks to be displayed on slider. Defaults to `{}`.\n    value (Optional[list[float]]): Default start and end value for slider. Must be 2 items. Defaults to `None`.\n    title (str): Title to be displayed. Defaults to `\"\"`.\n    actions (list[Action]): See [`Action`][vizro.models.Action]. Defaults to `[]`.",
       "properties": {
         "id": {
           "default": "",
@@ -1374,7 +1374,7 @@
     },
     "Slider": {
       "additionalProperties": false,
-      "description": "Numeric single-option selector `Slider`.\n\nCan be provided to [`Filter`][vizro.models.Filter] or\n[`Parameter`][vizro.models.Parameter]. Based on the underlying\n[`dcc.Slider`](https://dash.plotly.com/dash-core-components/slider).\n\nArgs:\n    type (Literal[\"range_slider\"]): Defaults to `\"range_slider\"`.\n    min (Optional[float]): Start value for slider. Defaults to `None`.\n    max (Optional[float]): End value for slider. Defaults to `None`.\n    step (Optional[float]): Step-size for marks on slider. Defaults to `None`.\n    marks (Optional[dict[float, str]]): Marks to be displayed on slider. Defaults to `{}`.\n    value (Optional[float]): Default value for slider. Defaults to `None`.\n    title (str): Title to be displayed. Defaults to `\"\"`.\n    actions (list[Action]): See [`Action`][vizro.models.Action]. Defaults to `[]`.",
+      "description": "Numeric single-option selector `Slider`.\n\nCan be provided to [`Filter`][vizro.models.Filter] or\n[`Parameter`][vizro.models.Parameter]. Based on the underlying\n[`dcc.Slider`](https://dash.plotly.com/dash-core-components/slider).\n\nArgs:\n    type (Literal[\"range_slider\"]): Defaults to `\"range_slider\"`.\n    min (Optional[float]): Start value for slider. Defaults to `None`.\n    max (Optional[float]): End value for slider. Defaults to `None`.\n    step (Optional[float]): Step-size for marks on slider. Defaults to `None`.\n    marks (Optional[dict[Union[float, int], str]]): Marks to be displayed on slider. Defaults to `{}`.\n    value (Optional[float]): Default value for slider. Defaults to `None`.\n    title (str): Title to be displayed. Defaults to `\"\"`.\n    actions (list[Action]): See [`Action`][vizro.models.Action]. Defaults to `[]`.",
       "properties": {
         "id": {
           "default": "",
diff --git a/vizro-core/src/vizro/models/_components/form/_form_utils.py b/vizro-core/src/vizro/models/_components/form/_form_utils.py
index 817b8d14b..dc369aa71 100644
--- a/vizro-core/src/vizro/models/_components/form/_form_utils.py
+++ b/vizro-core/src/vizro/models/_components/form/_form_utils.py
@@ -115,7 +115,7 @@ def validate_step(step, info: ValidationInfo):
 
 
 def set_default_marks(
-    marks: Optional[dict[Union[float, int], str]], info: ValidationInfo
+    marks: Optional[dict[float, str]], info: ValidationInfo
 ) -> Optional[dict[Union[float, int], str]]:
     if not marks and info.data.get("step") is None:
         marks = None
diff --git a/vizro-core/src/vizro/models/_components/form/range_slider.py b/vizro-core/src/vizro/models/_components/form/range_slider.py
index 5c7bff713..4a4651f65 100644
--- a/vizro-core/src/vizro/models/_components/form/range_slider.py
+++ b/vizro-core/src/vizro/models/_components/form/range_slider.py
@@ -46,7 +46,7 @@ class RangeSlider(VizroBaseModel):
         Field(default=None, description="Step-size for marks on slider."),
     ]
     marks: Annotated[
-        Optional[dict[Union[float, int], str]],
+        Optional[dict[float, str]],
         AfterValidator(set_default_marks),
         Field(default={}, description="Marks to be displayed on slider.", validate_default=True),
     ]
diff --git a/vizro-core/src/vizro/models/_components/form/slider.py b/vizro-core/src/vizro/models/_components/form/slider.py
index 486b65581..414b37d97 100644
--- a/vizro-core/src/vizro/models/_components/form/slider.py
+++ b/vizro-core/src/vizro/models/_components/form/slider.py
@@ -46,7 +46,7 @@ class Slider(VizroBaseModel):
         Field(default=None, description="Step-size for marks on slider."),
     ]
     marks: Annotated[
-        Optional[dict[Union[float, int], str]],
+        Optional[dict[float, str]],
         AfterValidator(set_default_marks),
         Field(default={}, description="Marks to be displayed on slider.", validate_default=True),
     ]
diff --git a/vizro-core/tests/unit/vizro/models/_components/form/test_range_slider.py b/vizro-core/tests/unit/vizro/models/_components/form/test_range_slider.py
index c9201100c..99e28fe30 100644
--- a/vizro-core/tests/unit/vizro/models/_components/form/test_range_slider.py
+++ b/vizro-core/tests/unit/vizro/models/_components/form/test_range_slider.py
@@ -240,7 +240,7 @@ def test_valid_marks(self, marks, expected):
             ]
 
     def test_invalid_marks(self):
-        with pytest.raises(ValidationError, match="6 validation errors for RangeSlider"):
+        with pytest.raises(ValidationError, match="4 validation errors for RangeSlider"):
             vm.RangeSlider(min=1, max=10, marks={"start": 0, "end": 10})
 
     @pytest.mark.parametrize("step, expected", [(1, {}), (None, None)])
diff --git a/vizro-core/tests/unit/vizro/models/_components/form/test_slider.py b/vizro-core/tests/unit/vizro/models/_components/form/test_slider.py
index 9e925ae5e..ebb7a7681 100755
--- a/vizro-core/tests/unit/vizro/models/_components/form/test_slider.py
+++ b/vizro-core/tests/unit/vizro/models/_components/form/test_slider.py
@@ -131,7 +131,7 @@ def test_valid_marks(self, marks, expected):
             ]
 
     def test_invalid_marks(self):
-        with pytest.raises(ValidationError, match="6 validation errors for Slider"):
+        with pytest.raises(ValidationError, match="4 validation errors for Slider"):
             vm.Slider(min=1, max=10, marks={"start": 0, "end": 10})
 
     @pytest.mark.parametrize("step, expected", [(1, {}), (None, None)])