diff --git a/algobattle/problem.py b/algobattle/problem.py
index 0fd3bd9b..65cabace 100644
--- a/algobattle/problem.py
+++ b/algobattle/problem.py
@@ -28,8 +28,13 @@
     GetCoreSchemaHandler,
     ValidationInfo,
 )
+from pydantic.main import BaseModel
 from pydantic_core import CoreSchema
-from pydantic_core.core_schema import with_info_after_validator_function
+from pydantic_core.core_schema import (
+    with_info_after_validator_function,
+    with_info_wrap_validator_function,
+    ValidatorFunctionWrapHandler,
+)
 
 from algobattle.util import (
     EncodableModel,
@@ -503,20 +508,22 @@ class InstanceSolutionModel(EncodableModel):
     """Base class for Instance and solution models."""
 
     @classmethod
-    def model_validate(  # noqa: D102
-        cls,
-        obj: Any,
-        *,
-        strict: bool | None = None,
-        from_attributes: bool | None = None,
-        context: dict[str, Any] | None = None,
-    ) -> Self:
-        model = super().model_validate(obj, strict=strict, from_attributes=from_attributes, context=context)
-        model_type = "instance" if issubclass(cls, InstanceModel) else "solution"
+    def __get_pydantic_core_schema__(cls, source: type[BaseModel], handler: GetCoreSchemaHandler) -> CoreSchema:
+        schema = handler(cls)
+        try:
+            model_type = "instance" if issubclass(cls, InstanceModel) else "solution"
+        except NameError:
+            return schema
         if cls._validate_with_self(model_type):
-            context = (context or {}) | {"self": model, model_type: model}
-            model = super().model_validate(obj, context=context)
-        return model
+
+            def validate_with_self(input: object, validate: ValidatorFunctionWrapHandler, info: ValidationInfo) -> Self:
+                self = validate(input)
+                if info.context is None or "self" not in info.context:
+                    self = cls.model_validate(input, context=(info.context or {}) | {"self": self, model_type: self})
+                return self
+
+            schema = with_info_wrap_validator_function(validate_with_self, schema)
+        return schema
 
     @classmethod
     def _annotation_needs_self(cls, annotation: object, model_type: ModelType) -> bool: