diff --git a/x-pack/plugin/mapper-aggregate-metric/src/main/java/org/elasticsearch/xpack/aggregatemetric/mapper/AggregateMetricDoubleFieldMapper.java b/x-pack/plugin/mapper-aggregate-metric/src/main/java/org/elasticsearch/xpack/aggregatemetric/mapper/AggregateMetricDoubleFieldMapper.java
index e04aa5f6ad157..587086765c46a 100644
--- a/x-pack/plugin/mapper-aggregate-metric/src/main/java/org/elasticsearch/xpack/aggregatemetric/mapper/AggregateMetricDoubleFieldMapper.java
+++ b/x-pack/plugin/mapper-aggregate-metric/src/main/java/org/elasticsearch/xpack/aggregatemetric/mapper/AggregateMetricDoubleFieldMapper.java
@@ -31,7 +31,6 @@
 import org.elasticsearch.index.mapper.DocumentParserContext;
 import org.elasticsearch.index.mapper.FieldMapper;
 import org.elasticsearch.index.mapper.IgnoreMalformedStoredValues;
-import org.elasticsearch.index.mapper.IndexType;
 import org.elasticsearch.index.mapper.MappedFieldType;
 import org.elasticsearch.index.mapper.Mapper;
 import org.elasticsearch.index.mapper.MapperBuilderContext;
@@ -253,11 +252,11 @@ public AggregateMetricDoubleFieldMapper build(MapperBuilderContext context) {
 
             AggregateMetricDoubleFieldType metricFieldType = new AggregateMetricDoubleFieldType(
                 context.buildFullName(leafName()),
-                meta.getValue(),
-                timeSeriesMetric.getValue()
+                timeSeriesMetric.getValue(),
+                defaultMetric.getValue(),
+                metricFields,
+                meta.getValue()
             );
-            metricFieldType.setMetricFields(metricFields);
-            metricFieldType.setDefaultMetric(defaultMetric.getValue());
 
             return new AggregateMetricDoubleFieldMapper(leafName(), metricFieldType, metricMappers, builderParams(this, context), this);
         }
@@ -270,19 +269,21 @@ public AggregateMetricDoubleFieldMapper build(MapperBuilderContext context) {
 
     public static final class AggregateMetricDoubleFieldType extends SimpleMappedFieldType {
 
-        private EnumMap<Metric, NumberFieldMapper.NumberFieldType> metricFields;
-
-        private Metric defaultMetric;
-
+        private final EnumMap<Metric, NumberFieldMapper.NumberFieldType> metricFields;
+        private final Metric defaultMetric;
         private final MetricType metricType;
 
-        public AggregateMetricDoubleFieldType(String name) {
-            this(name, Collections.emptyMap(), null);
-        }
-
-        public AggregateMetricDoubleFieldType(String name, Map<String, String> meta, MetricType metricType) {
-            super(name, IndexType.points(true, true), false, meta);
+        public AggregateMetricDoubleFieldType(
+            String name,
+            MetricType metricType,
+            Metric defaultMetric,
+            EnumMap<Metric, NumberFieldMapper.NumberFieldType> metricFields,
+            Map<String, String> meta
+        ) {
+            super(name, metricFields.get(defaultMetric).indexType(), false, meta);
             this.metricType = metricType;
+            this.defaultMetric = defaultMetric;
+            this.metricFields = metricFields;
         }
 
         /**
@@ -311,29 +312,10 @@ public TextSearchInfo getTextSearchInfo() {
             return TextSearchInfo.SIMPLE_MATCH_WITHOUT_TERMS;
         }
 
-        private void setMetricFields(EnumMap<Metric, NumberFieldMapper.NumberFieldType> metricFields) {
-            this.metricFields = metricFields;
-        }
-
         public Map<Metric, NumberFieldMapper.NumberFieldType> getMetricFields() {
             return Collections.unmodifiableMap(metricFields);
         }
 
-        public void addMetricField(Metric m, NumberFieldMapper.NumberFieldType subfield) {
-            if (metricFields == null) {
-                metricFields = new EnumMap<>(AggregateMetricDoubleFieldMapper.Metric.class);
-            }
-
-            if (name() == null) {
-                throw new IllegalArgumentException("Field of type [" + typeName() + "] must have a name before adding a subfield");
-            }
-            metricFields.put(m, subfield);
-        }
-
-        public void setDefaultMetric(Metric defaultMetric) {
-            this.defaultMetric = defaultMetric;
-        }
-
         Metric getDefaultMetric() {
             return defaultMetric;
         }
diff --git a/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedAvgAggregatorTests.java b/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedAvgAggregatorTests.java
index fade3f68376d0..530aea03c781e 100644
--- a/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedAvgAggregatorTests.java
+++ b/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedAvgAggregatorTests.java
@@ -31,7 +31,9 @@
 import org.elasticsearch.xpack.aggregatemetric.mapper.AggregateMetricDoubleFieldMapper.Metric;
 
 import java.io.IOException;
+import java.util.EnumMap;
 import java.util.List;
+import java.util.Map;
 import java.util.function.Consumer;
 
 import static java.util.Collections.singleton;
@@ -117,18 +119,16 @@ public void testQueryFiltering() throws IOException {
      * @return the created field type
      */
     private AggregateMetricDoubleFieldType createDefaultFieldType(String fieldName) {
-        AggregateMetricDoubleFieldType fieldType = new AggregateMetricDoubleFieldType(fieldName);
-
+        EnumMap<Metric, NumberFieldMapper.NumberFieldType> metricFields = new EnumMap<>(Metric.class);
         for (Metric m : List.of(Metric.value_count, Metric.sum)) {
             String subfieldName = subfieldName(fieldName, m);
             NumberFieldMapper.NumberFieldType subfield = new NumberFieldMapper.NumberFieldType(
                 subfieldName,
                 NumberFieldMapper.NumberType.DOUBLE
             );
-            fieldType.addMetricField(m, subfield);
+            metricFields.put(m, subfield);
         }
-        fieldType.setDefaultMetric(Metric.sum);
-        return fieldType;
+        return new AggregateMetricDoubleFieldType(fieldName, null, Metric.sum, metricFields, Map.of());
     }
 
     private void testCase(Query query, CheckedConsumer<RandomIndexWriter, IOException> buildIndex, Consumer<InternalAvg> verify)
diff --git a/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedMaxAggregatorTests.java b/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedMaxAggregatorTests.java
index 33e9151773fc2..1f04f89c8f5eb 100644
--- a/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedMaxAggregatorTests.java
+++ b/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedMaxAggregatorTests.java
@@ -31,7 +31,9 @@
 import org.elasticsearch.xpack.aggregatemetric.mapper.AggregateMetricDoubleFieldMapper.Metric;
 
 import java.io.IOException;
+import java.util.EnumMap;
 import java.util.List;
+import java.util.Map;
 import java.util.function.Consumer;
 
 import static java.util.Collections.singleton;
@@ -117,18 +119,16 @@ public void testQueryFiltering() throws IOException {
      * @return the created field type
      */
     private AggregateMetricDoubleFieldType createDefaultFieldType(String fieldName) {
-        AggregateMetricDoubleFieldType fieldType = new AggregateMetricDoubleFieldType(fieldName);
-
+        EnumMap<Metric, NumberFieldMapper.NumberFieldType> metricFields = new EnumMap<>(Metric.class);
         for (Metric m : List.of(Metric.min, Metric.max)) {
             String subfieldName = subfieldName(fieldName, m);
             NumberFieldMapper.NumberFieldType subfield = new NumberFieldMapper.NumberFieldType(
                 subfieldName,
                 NumberFieldMapper.NumberType.DOUBLE
             );
-            fieldType.addMetricField(m, subfield);
+            metricFields.put(m, subfield);
         }
-        fieldType.setDefaultMetric(Metric.min);
-        return fieldType;
+        return new AggregateMetricDoubleFieldType(fieldName, null, Metric.min, metricFields, Map.of());
     }
 
     private void testCase(Query query, CheckedConsumer<RandomIndexWriter, IOException> buildIndex, Consumer<Max> verify)
diff --git a/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedMinAggregatorTests.java b/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedMinAggregatorTests.java
index 0f655b90a2358..adf138cc8f4f1 100644
--- a/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedMinAggregatorTests.java
+++ b/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedMinAggregatorTests.java
@@ -31,7 +31,9 @@
 import org.elasticsearch.xpack.aggregatemetric.mapper.AggregateMetricDoubleFieldMapper.Metric;
 
 import java.io.IOException;
+import java.util.EnumMap;
 import java.util.List;
+import java.util.Map;
 import java.util.function.Consumer;
 
 import static java.util.Collections.singleton;
@@ -117,18 +119,16 @@ public void testQueryFiltering() throws IOException {
      * @return the created field type
      */
     private AggregateMetricDoubleFieldType createDefaultFieldType(String fieldName) {
-        AggregateMetricDoubleFieldType fieldType = new AggregateMetricDoubleFieldType(fieldName);
-
+        EnumMap<Metric, NumberFieldMapper.NumberFieldType> metricFields = new EnumMap<>(Metric.class);
         for (Metric m : List.of(Metric.min, Metric.max)) {
             String subfieldName = subfieldName(fieldName, m);
             NumberFieldMapper.NumberFieldType subfield = new NumberFieldMapper.NumberFieldType(
                 subfieldName,
                 NumberFieldMapper.NumberType.DOUBLE
             );
-            fieldType.addMetricField(m, subfield);
+            metricFields.put(m, subfield);
         }
-        fieldType.setDefaultMetric(Metric.min);
-        return fieldType;
+        return new AggregateMetricDoubleFieldType(fieldName, null, Metric.min, metricFields, Map.of());
     }
 
     private void testCase(Query query, CheckedConsumer<RandomIndexWriter, IOException> buildIndex, Consumer<Min> verify)
diff --git a/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedSumAggregatorTests.java b/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedSumAggregatorTests.java
index e0e421189497c..7d015d3a8efa6 100644
--- a/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedSumAggregatorTests.java
+++ b/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedSumAggregatorTests.java
@@ -31,7 +31,9 @@
 import org.elasticsearch.xpack.aggregatemetric.mapper.AggregateMetricDoubleFieldMapper.Metric;
 
 import java.io.IOException;
+import java.util.EnumMap;
 import java.util.List;
+import java.util.Map;
 import java.util.function.Consumer;
 
 import static java.util.Collections.singleton;
@@ -117,18 +119,16 @@ public void testQueryFiltering() throws IOException {
      * @return the created field type
      */
     private AggregateMetricDoubleFieldType createDefaultFieldType(String fieldName) {
-        AggregateMetricDoubleFieldType fieldType = new AggregateMetricDoubleFieldType(fieldName);
-
+        EnumMap<Metric, NumberFieldMapper.NumberFieldType> metricFields = new EnumMap<>(Metric.class);
         for (Metric m : List.of(Metric.value_count, Metric.sum)) {
             String subfieldName = subfieldName(fieldName, m);
             NumberFieldMapper.NumberFieldType subfield = new NumberFieldMapper.NumberFieldType(
                 subfieldName,
                 NumberFieldMapper.NumberType.DOUBLE
             );
-            fieldType.addMetricField(m, subfield);
+            metricFields.put(m, subfield);
         }
-        fieldType.setDefaultMetric(Metric.sum);
-        return fieldType;
+        return new AggregateMetricDoubleFieldType(fieldName, null, Metric.sum, metricFields, Map.of());
     }
 
     private void testCase(Query query, CheckedConsumer<RandomIndexWriter, IOException> buildIndex, Consumer<Sum> verify)
diff --git a/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedValueCountAggregatorTests.java b/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedValueCountAggregatorTests.java
index dbae604b8f725..227a69257d31f 100644
--- a/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedValueCountAggregatorTests.java
+++ b/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/aggregations/metrics/AggregateMetricBackedValueCountAggregatorTests.java
@@ -31,7 +31,9 @@
 import org.elasticsearch.xpack.aggregatemetric.mapper.AggregateMetricDoubleFieldMapper.Metric;
 
 import java.io.IOException;
+import java.util.EnumMap;
 import java.util.List;
+import java.util.Map;
 import java.util.function.Consumer;
 
 import static java.util.Collections.singleton;
@@ -116,18 +118,16 @@ public void testQueryFiltering() throws IOException {
      * @return the created field type
      */
     private AggregateMetricDoubleFieldType createDefaultFieldType(String fieldName) {
-        AggregateMetricDoubleFieldType fieldType = new AggregateMetricDoubleFieldType(fieldName);
-
+        EnumMap<Metric, NumberFieldMapper.NumberFieldType> metricFields = new EnumMap<>(Metric.class);
         for (Metric m : List.of(Metric.value_count, Metric.sum)) {
             String subfieldName = subfieldName(fieldName, m);
             NumberFieldMapper.NumberFieldType subfield = new NumberFieldMapper.NumberFieldType(
                 subfieldName,
                 NumberFieldMapper.NumberType.DOUBLE
             );
-            fieldType.addMetricField(m, subfield);
+            metricFields.put(m, subfield);
         }
-        fieldType.setDefaultMetric(Metric.sum);
-        return fieldType;
+        return new AggregateMetricDoubleFieldType(fieldName, null, Metric.sum, metricFields, Map.of());
     }
 
     private void testCase(Query query, CheckedConsumer<RandomIndexWriter, IOException> buildIndex, Consumer<InternalValueCount> verify)
diff --git a/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/mapper/AggregateMetricDoubleFieldTypeTests.java b/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/mapper/AggregateMetricDoubleFieldTypeTests.java
index 55ecfc13b1f3e..87495ba84381e 100644
--- a/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/mapper/AggregateMetricDoubleFieldTypeTests.java
+++ b/x-pack/plugin/mapper-aggregate-metric/src/test/java/org/elasticsearch/xpack/aggregatemetric/mapper/AggregateMetricDoubleFieldTypeTests.java
@@ -32,6 +32,7 @@
 
 import java.io.IOException;
 import java.util.Collections;
+import java.util.EnumMap;
 import java.util.List;
 import java.util.Map;
 
@@ -46,20 +47,16 @@
 public class AggregateMetricDoubleFieldTypeTests extends FieldTypeTestCase {
 
     protected AggregateMetricDoubleFieldType createDefaultFieldType(String name, Map<String, String> meta, Metric defaultMetric) {
-        AggregateMetricDoubleFieldType fieldType = new AggregateMetricDoubleFieldType(name, meta, null);
-        for (AggregateMetricDoubleFieldMapper.Metric m : List.of(
-            AggregateMetricDoubleFieldMapper.Metric.min,
-            AggregateMetricDoubleFieldMapper.Metric.max
-        )) {
-            String subfieldName = subfieldName(fieldType.name(), m);
+        EnumMap<Metric, NumberFieldMapper.NumberFieldType> metricFields = new EnumMap<>(Metric.class);
+        for (Metric m : List.of(Metric.min, Metric.max)) {
+            String subfieldName = subfieldName(name, m);
             NumberFieldMapper.NumberFieldType subfield = new NumberFieldMapper.NumberFieldType(
                 subfieldName,
                 NumberFieldMapper.NumberType.DOUBLE
             );
-            fieldType.addMetricField(m, subfield);
+            metricFields.put(m, subfield);
         }
-        fieldType.setDefaultMetric(defaultMetric);
-        return fieldType;
+        return new AggregateMetricDoubleFieldType(name, null, defaultMetric, metricFields, meta);
     }
 
     public void testTermQuery() {