diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/AbstractLuceneMetricNumericFieldAggregation.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/AbstractLuceneMetricNumericFieldAggregation.java
index c9423156a82..b2823f21674 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/AbstractLuceneMetricNumericFieldAggregation.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/AbstractLuceneMetricNumericFieldAggregation.java
@@ -20,7 +20,6 @@
 import org.hibernate.search.engine.cfg.spi.NumberUtils;
 import org.hibernate.search.engine.search.aggregation.spi.FieldMetricAggregationBuilder;
 import org.hibernate.search.engine.search.common.ValueModel;
-import org.hibernate.search.util.common.AssertionFailure;
 
 /**
  * @param <F> The type of field values.
@@ -93,19 +92,16 @@ public K extract(AggregationExtractContext context) {
 		}
 	}
 
-	protected static class TypeSelector<F> implements FieldMetricAggregationBuilder.TypeSelector {
-		private final AbstractLuceneNumericFieldCodec<F, ?> codec;
-		private final LuceneSearchIndexScope<?> scope;
-		private final LuceneSearchIndexValueFieldContext<F> field;
-		private final String operation;
+	protected abstract static class TypeSelector<F> implements FieldMetricAggregationBuilder.TypeSelector {
+		protected final AbstractLuceneNumericFieldCodec<F, ?> codec;
+		protected final LuceneSearchIndexScope<?> scope;
+		protected final LuceneSearchIndexValueFieldContext<F> field;
 
 		protected TypeSelector(AbstractLuceneNumericFieldCodec<F, ?> codec,
-				LuceneSearchIndexScope<?> scope, LuceneSearchIndexValueFieldContext<F> field,
-				String operation) {
+				LuceneSearchIndexScope<?> scope, LuceneSearchIndexValueFieldContext<F> field) {
 			this.codec = codec;
 			this.scope = scope;
 			this.field = field;
-			this.operation = operation;
 		}
 
 		@Override
@@ -118,22 +114,11 @@ protected TypeSelector(AbstractLuceneNumericFieldCodec<F, ?> codec,
 						.withConvertedType( expectedType, field );
 			}
 
-			if ( "sum".equals( operation ) ) {
-				return new LuceneSumNumericFieldAggregation.Builder<>( codec, scope, field, projectionConverter );
-			}
-			else if ( "min".equals( operation ) ) {
-				return new LuceneMinNumericFieldAggregation.Builder<>( codec, scope, field, projectionConverter );
-			}
-			else if ( "max".equals( operation ) ) {
-				return new LuceneMaxNumericFieldAggregation.Builder<>( codec, scope, field, projectionConverter );
-			}
-			else if ( "avg".equals( operation ) ) {
-				return new LuceneAvgNumericFieldAggregation.Builder<>( codec, scope, field, projectionConverter );
-			}
-			else {
-				throw new AssertionFailure( "Aggregation operation not supported: " + operation );
-			}
+			return getFtBuilder( projectionConverter );
 		}
+
+		protected abstract <T> Builder<F, ? extends Number, T> getFtBuilder(
+				ProjectionConverter<F, ? extends T> projectionConverter);
 	}
 
 	protected abstract static class Builder<F, E extends Number, K> extends AbstractBuilder<K>
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneAvgNumericFieldAggregation.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneAvgNumericFieldAggregation.java
index 12f1abe95e8..ed0f5c98b52 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneAvgNumericFieldAggregation.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneAvgNumericFieldAggregation.java
@@ -48,7 +48,22 @@ protected Factory(AbstractLuceneNumericFieldCodec<F, ?> codec) {
 		@Override
 		public FieldMetricAggregationBuilder.TypeSelector create(LuceneSearchIndexScope<?> scope,
 				LuceneSearchIndexValueFieldContext<F> field) {
-			return new TypeSelector<>( codec, scope, field, "avg" );
+			return new FunctionTypeSelector<>( codec, scope, field );
+		}
+	}
+
+	protected static class FunctionTypeSelector<F> extends TypeSelector<F>
+			implements FieldMetricAggregationBuilder.TypeSelector {
+
+		protected FunctionTypeSelector(AbstractLuceneNumericFieldCodec<F, ?> codec, LuceneSearchIndexScope<?> scope,
+				LuceneSearchIndexValueFieldContext<F> field) {
+			super( codec, scope, field );
+		}
+
+		@Override
+		protected <T> Builder<F, ? extends Number, T> getFtBuilder(
+				ProjectionConverter<F, ? extends T> projectionConverter) {
+			return new Builder<>( codec, scope, field, projectionConverter );
 		}
 	}
 
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneMaxNumericFieldAggregation.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneMaxNumericFieldAggregation.java
index 54f36b8e0fa..33829737b32 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneMaxNumericFieldAggregation.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneMaxNumericFieldAggregation.java
@@ -44,7 +44,22 @@ protected Factory(AbstractLuceneNumericFieldCodec<F, ?> codec) {
 		@Override
 		public FieldMetricAggregationBuilder.TypeSelector create(LuceneSearchIndexScope<?> scope,
 				LuceneSearchIndexValueFieldContext<F> field) {
-			return new TypeSelector<>( codec, scope, field, "max" );
+			return new FunctionTypeSelector<>( codec, scope, field );
+		}
+	}
+
+	protected static class FunctionTypeSelector<F> extends TypeSelector<F>
+			implements FieldMetricAggregationBuilder.TypeSelector {
+
+		protected FunctionTypeSelector(AbstractLuceneNumericFieldCodec<F, ?> codec, LuceneSearchIndexScope<?> scope,
+				LuceneSearchIndexValueFieldContext<F> field) {
+			super( codec, scope, field );
+		}
+
+		@Override
+		protected <T> Builder<F, ? extends Number, T> getFtBuilder(
+				ProjectionConverter<F, ? extends T> projectionConverter) {
+			return new Builder<>( codec, scope, field, projectionConverter );
 		}
 	}
 
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneMinNumericFieldAggregation.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneMinNumericFieldAggregation.java
index 458c3c504bd..70bbd260518 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneMinNumericFieldAggregation.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneMinNumericFieldAggregation.java
@@ -44,7 +44,22 @@ protected Factory(AbstractLuceneNumericFieldCodec<F, ?> codec) {
 		@Override
 		public FieldMetricAggregationBuilder.TypeSelector create(LuceneSearchIndexScope<?> scope,
 				LuceneSearchIndexValueFieldContext<F> field) {
-			return new TypeSelector<>( codec, scope, field, "min" );
+			return new FunctionTypeSelector<>( codec, scope, field );
+		}
+	}
+
+	protected static class FunctionTypeSelector<F> extends TypeSelector<F>
+			implements FieldMetricAggregationBuilder.TypeSelector {
+
+		protected FunctionTypeSelector(AbstractLuceneNumericFieldCodec<F, ?> codec, LuceneSearchIndexScope<?> scope,
+				LuceneSearchIndexValueFieldContext<F> field) {
+			super( codec, scope, field );
+		}
+
+		@Override
+		protected <T> Builder<F, ? extends Number, T> getFtBuilder(
+				ProjectionConverter<F, ? extends T> projectionConverter) {
+			return new Builder<>( codec, scope, field, projectionConverter );
 		}
 	}
 
diff --git a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneSumNumericFieldAggregation.java b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneSumNumericFieldAggregation.java
index f2a7e1c715c..3630e971016 100644
--- a/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneSumNumericFieldAggregation.java
+++ b/backend/lucene/src/main/java/org/hibernate/search/backend/lucene/types/aggregation/impl/LuceneSumNumericFieldAggregation.java
@@ -44,7 +44,22 @@ protected Factory(AbstractLuceneNumericFieldCodec<F, ?> codec) {
 		@Override
 		public FieldMetricAggregationBuilder.TypeSelector create(LuceneSearchIndexScope<?> scope,
 				LuceneSearchIndexValueFieldContext<F> field) {
-			return new TypeSelector<>( codec, scope, field, "sum" );
+			return new FunctionTypeSelector<>( codec, scope, field );
+		}
+	}
+
+	protected static class FunctionTypeSelector<F> extends TypeSelector<F>
+			implements FieldMetricAggregationBuilder.TypeSelector {
+
+		protected FunctionTypeSelector(AbstractLuceneNumericFieldCodec<F, ?> codec, LuceneSearchIndexScope<?> scope,
+				LuceneSearchIndexValueFieldContext<F> field) {
+			super( codec, scope, field );
+		}
+
+		@Override
+		protected <T> Builder<F, ? extends Number, T> getFtBuilder(
+				ProjectionConverter<F, ? extends T> projectionConverter) {
+			return new Builder<>( codec, scope, field, projectionConverter );
 		}
 	}