diff --git a/gns3server/schemas/controller/appliances.py b/gns3server/schemas/controller/appliances.py
index 16a9810ea..ee221e788 100644
--- a/gns3server/schemas/controller/appliances.py
+++ b/gns3server/schemas/controller/appliances.py
@@ -19,9 +19,7 @@
 from enum import Enum
 from typing import Annotated, List, Literal, Optional, Union
 from uuid import UUID
-
-from pydantic import AnyUrl, BaseModel, Discriminator, EmailStr, Field, Tag, model_validator
-
+from pydantic import AnyUrl, BaseModel, Discriminator, EmailStr, Field, Tag
 from ..common import ExtraConfig
 
 # ============================================================================
@@ -599,45 +597,38 @@ class QemuPropertiesV8(BaseModel):
     process_priority: Optional[QemuProcessPriority] = Field(None, title="Process priority for QEMU")
 
 
-_V8_PROPERTIES_MODELS = {
-    TemplateType.qemu: QemuPropertiesV8,
-    TemplateType.dynamips: DynamipsPropertiesV8,
-    TemplateType.iou: IouPropertiesV8,
-    TemplateType.docker: DockerPropertiesV8,
-}
-
-
-class TemplateSetting(BaseModel):
+class TemplateSettingBase(BaseModel):
     """Emulator settings configuration (v8)"""
 
     name: Optional[str] = Field(None, title="Name of the settings set")
     default: Optional[bool] = Field(None, title="Whether these are the default settings")
     inherit_default_properties: Optional[bool] = Field(True, title="Whether the default properties should be used")
-    template_type: TemplateType = Field(..., title="Type of emulator properties")
-    template_properties: Union[QemuPropertiesV8, DynamipsPropertiesV8, IouPropertiesV8, DockerPropertiesV8] = Field(
-        ..., title="Properties for the template"
-    )
 
-    @model_validator(mode="before")
-    @classmethod
-    def _validate_template_properties(cls, data):
-        """
-        Validate template_properties against the model matching template_type.
-        The template_type discriminator lives at the settings level (not inside
-        template_properties), so the union cannot be discriminated by pydantic
-        alone and would misroute properties between the per-type models.
-        """
 
-        if isinstance(data, dict):
-            # work on a copy: replacing template_properties with the validated
-            # model must not mutate the caller's data
-            data = data.copy()
-            template_type = data.get("template_type")
-            template_properties = data.get("template_properties")
-            model = _V8_PROPERTIES_MODELS.get(template_type)
-            if model is not None and isinstance(template_properties, dict):
-                data["template_properties"] = model.model_validate(template_properties)
-        return data
+class QemuTemplateSetting(TemplateSettingBase):
+    template_type: Literal[TemplateType.qemu] = Field(..., title="Type of emulator properties")
+    template_properties: QemuPropertiesV8 = Field(..., title="Properties for the template")
+
+
+class DynamipsTemplateSetting(TemplateSettingBase):
+    template_type: Literal[TemplateType.dynamips] = Field(..., title="Type of emulator properties")
+    template_properties: DynamipsPropertiesV8 = Field(..., title="Properties for the template")
+
+
+class IouTemplateSetting(TemplateSettingBase):
+    template_type: Literal[TemplateType.iou] = Field(..., title="Type of emulator properties")
+    template_properties: IouPropertiesV8 = Field(..., title="Properties for the template")
+
+
+class DockerTemplateSetting(TemplateSettingBase):
+    template_type: Literal[TemplateType.docker] = Field(..., title="Type of emulator properties")
+    template_properties: DockerPropertiesV8 = Field(..., title="Properties for the template")
+
+
+TemplateSetting = Annotated[
+    Union[QemuTemplateSetting, DynamipsTemplateSetting, IouTemplateSetting, DockerTemplateSetting],
+    Field(discriminator="template_type"),
+]
 
 
 class ApplianceVersionV8(BaseModel):
diff --git a/tests/controller/test_appliance.py b/tests/controller/test_appliance.py
index b18a6cb97..0ec004e20 100644
--- a/tests/controller/test_appliance.py
+++ b/tests/controller/test_appliance.py
@@ -166,6 +166,32 @@ def test_v8_template_properties_validated_against_template_type():
         ApplianceModel.model_validate(appliance)
 
 
+def test_v8_unknown_template_type_is_discriminator_error():
+    appliance = dict(
+        XRD_V8,
+        settings=[{"name": "only", "default": True, "template_type": "vmware", "template_properties": {}}],
+    )
+    with pytest.raises(pydantic.ValidationError) as exc_info:
+        ApplianceModel.model_validate(appliance)
+    errors = exc_info.value.errors()
+    assert len(errors) == 1
+    assert errors[0]["type"] == "union_tag_invalid"
+
+
+def test_v8_invalid_properties_report_only_matching_type():
+    appliance = dict(
+        XRD_V8,
+        settings=[
+            {"name": "only", "default": True, "template_type": "docker", "template_properties": {"adapters": 2}},
+        ],
+    )
+    with pytest.raises(pydantic.ValidationError) as exc_info:
+        ApplianceModel.model_validate(appliance)
+    locs = [error["loc"] for error in exc_info.value.errors()]
+    assert all("docker" in loc for loc in locs)
+    assert any(loc[-1] == "image" for loc in locs)
+
+
 def test_v8_qemu_kvm_property_validates():
     appliance = dict(
         XRD_V8,