diff --git a/aligned/compiler/aggregation_factory.py b/aligned/compiler/aggregation_factory.py
index 72e5d822..d701bfff 100644
--- a/aligned/compiler/aggregation_factory.py
+++ b/aligned/compiler/aggregation_factory.py
@@ -349,6 +349,11 @@ class PolarsTransformationFactoryAggregation(TransformationFactory, AggregationT
     def using_features(self) -> list[FeatureFactory]:
         return self._using_features
 
+    def aggregate_over(
+        self, group_by: list[FeatureReferance], time_column: FeatureReferance | None
+    ) -> AggregateOver:
+        return aggregate_over(group_by, time_column, None, None, None, None)
+
     def compile(self) -> Transformation:
         import inspect
         import types
@@ -358,10 +363,9 @@ def compile(self) -> Transformation:
         from aligned.schemas.transformation import PolarsFunctionTransformation, PolarsLambdaTransformation
 
         if isinstance(self.method, pl.Expr):
-            code = str(self.method)
-            return PolarsLambdaTransformation(
-                method=dill.dumps(self.method), code=code.strip(), dtype=self.dtype.dtype
-            )
+            method = lambda df, alias: self.method  # type: ignore
+            code = ''
+            return PolarsLambdaTransformation(method=dill.dumps(method), code=code, dtype=self.dtype.dtype)
         else:
             code = inspect.getsource(self.method)
 
diff --git a/aligned/compiler/feature_factory.py b/aligned/compiler/feature_factory.py
index bdcf0ae2..710e2950 100644
--- a/aligned/compiler/feature_factory.py
+++ b/aligned/compiler/feature_factory.py
@@ -517,6 +517,26 @@ def transform_polars(
         dtype.transformation = PolarsTransformationFactory(dtype, expression, using_features or [self])
         return dtype  # type: ignore [return-value]
 
+    def polars_aggregation(self, aggregation: pl.Expr, as_type: T) -> T:
+        from aligned.compiler.aggregation_factory import PolarsTransformationFactoryAggregation
+
+        value = as_type.copy_type()  # type: ignore [assignment]
+        value.transformation = PolarsTransformationFactoryAggregation(as_type, aggregation, [self])
+
+        return value
+
+    def polars_aggregation_using_features(
+        self: T,
+        using_features: list[FeatureFactory],
+        aggregation: pl.Expr,
+    ) -> T:
+        from aligned.compiler.aggregation_factory import PolarsTransformationFactoryAggregation
+
+        value = self.copy_type()  # type: ignore [assignment]
+        value.transformation = PolarsTransformationFactoryAggregation(self, aggregation, using_features)
+
+        return value
+
     def is_required(self: T) -> T:
         return self
 
diff --git a/aligned/tests/test_transformations.py b/aligned/tests/test_transformations.py
index ea009bab..d2894fbb 100644
--- a/aligned/tests/test_transformations.py
+++ b/aligned/tests/test_transformations.py
@@ -1,5 +1,5 @@
 import pytest
-from aligned.compiler.feature_factory import EventTimestamp, Int32, String
+from aligned.compiler.feature_factory import EventTimestamp, Int32, String, Float
 
 from aligned.feature_store import FeatureStore
 from aligned.feature_view.feature_view import feature_view
@@ -54,6 +54,8 @@ class TestAgg:
 
 @pytest.mark.asyncio
 async def test_aggregations_on_all_no_window() -> None:
+    import polars as pl
+
     @feature_view(name='test_agg', source=FileSource.parquet_at('test_data/credit_history.parquet'))
     class TestAgg:
         dob_ssn = String().as_entity()
@@ -66,9 +68,26 @@ class TestAgg:
         credit_card_due_sum = credit_card_due.aggregate().sum()
         student_loan_due_mean = student_loan_due.aggregate().mean()
 
+        custom_mean_aggregation = student_loan_due.polars_aggregation(
+            pl.col('student_loan_due').mean(),
+            as_type=Float(),
+        )
+        custom_mean_aggregation_using_features = Float().polars_aggregation_using_features(
+            using_features=[student_loan_due],
+            aggregation=pl.col('student_loan_due').mean(),
+        )
+        custom_sum_aggregation = credit_card_due.polars_aggregation(
+            pl.col('credit_card_due').sum(),
+            as_type=Float(),
+        )
+
     df = await TestAgg.query().all().to_pandas()  # type: ignore
     assert df.shape[0] == 3
 
+    assert df['custom_mean_aggregation'].equals(df['student_loan_due_mean'])
+    assert df['custom_mean_aggregation'].equals(df['custom_mean_aggregation_using_features'])
+    assert df['custom_sum_aggregation'].equals(df['credit_card_due_sum'])
+
 
 @pytest.mark.asyncio
 async def test_aggregations_on_all_no_window_materialised() -> None:
diff --git a/pyproject.toml b/pyproject.toml
index 47dddf10..f1783979 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "aligned"
-version = "0.0.62"
+version = "0.0.63"
 description = "A data managment and lineage tool for ML applications."
 authors = ["Mats E. Mollestad <mats@mollestad.no>"]
 license = "Apache-2.0"