diff --git a/data/beaconrestapi/src/integration-test/resources/tech/pegasys/teku/beaconrestapi/beacon/paths/_eth_v1_debug_fork_choice.json b/data/beaconrestapi/src/integration-test/resources/tech/pegasys/teku/beaconrestapi/beacon/paths/_eth_v1_debug_fork_choice.json
index 7657d7ee73c..c0d7bfb15f2 100644
--- a/data/beaconrestapi/src/integration-test/resources/tech/pegasys/teku/beaconrestapi/beacon/paths/_eth_v1_debug_fork_choice.json
+++ b/data/beaconrestapi/src/integration-test/resources/tech/pegasys/teku/beaconrestapi/beacon/paths/_eth_v1_debug_fork_choice.json
@@ -63,7 +63,7 @@
                       },
                       "validity" : {
                         "type" : "string",
-                        "enum" : [ "VALID", "INVALID", "OPTIMISTIC" ]
+                        "enum" : [ "valid", "invalid", "optimistic" ]
                       },
                       "execution_block_hash" : {
                         "type" : "string",
diff --git a/data/beaconrestapi/src/main/java/tech/pegasys/teku/beaconrestapi/handlers/v1/debug/GetForkChoice.java b/data/beaconrestapi/src/main/java/tech/pegasys/teku/beaconrestapi/handlers/v1/debug/GetForkChoice.java
index cd051969a9c..439af4e1f37 100644
--- a/data/beaconrestapi/src/main/java/tech/pegasys/teku/beaconrestapi/handlers/v1/debug/GetForkChoice.java
+++ b/data/beaconrestapi/src/main/java/tech/pegasys/teku/beaconrestapi/handlers/v1/debug/GetForkChoice.java
@@ -72,7 +72,7 @@ public class GetForkChoice extends RestApiEndpoint {
               .withField("weight", UINT64_TYPE, ProtoNodeData::getWeight)
               .withField(
                   "validity",
-                  DeserializableTypeDefinition.enumOf(ProtoNodeValidationStatus.class),
+                  DeserializableTypeDefinition.enumOf(ProtoNodeValidationStatus.class, true),
                   ProtoNodeData::getValidationStatus)
               .withField(
                   "execution_block_hash",
diff --git a/data/beaconrestapi/src/test/resources/tech/pegasys/teku/beaconrestapi/handlers/v1/debug/getForkChoice.json b/data/beaconrestapi/src/test/resources/tech/pegasys/teku/beaconrestapi/handlers/v1/debug/getForkChoice.json
index c6f0ec4ceb7..a1e65ee71b2 100644
--- a/data/beaconrestapi/src/test/resources/tech/pegasys/teku/beaconrestapi/handlers/v1/debug/getForkChoice.json
+++ b/data/beaconrestapi/src/test/resources/tech/pegasys/teku/beaconrestapi/handlers/v1/debug/getForkChoice.json
@@ -1 +1 @@
-{"justified_checkpoint":{"epoch":"1","root":"0x0000000000000000000000000000000000000000000000000000000000001111"},"finalized_checkpoint":{"epoch":"0","root":"0x0000000000000000000000000000000000000000000000000000000000002222"},"fork_choice_nodes":[{"slot":"32","block_root":"0x0000000000000000000000000000000000000000000000000000000000003333","parent_root":"0x0000000000000000000000000000000000000000000000000000000000004444","justified_epoch":"10","finalized_epoch":"11","weight":"409600000000","validity":"OPTIMISTIC","execution_block_hash":"0x0000000000000000000000000000000000000000000000000000000000006666","extra_data":{"state_root":"0x0000000000000000000000000000000000000000000000000000000000005555","justified_root":"0x0000000000000000000000000000000000000000000000000000000000007777","unrealised_justified_epoch":"12","unrealized_justified_root":"0x0000000000000000000000000000000000000000000000000000000000009999","unrealised_finalized_epoch":"13","unrealized_finalized_root":"0x0000000000000000000000000000000000000000000000000000000000000000"}}],"extra_data":{}}
\ No newline at end of file
+{"justified_checkpoint":{"epoch":"1","root":"0x0000000000000000000000000000000000000000000000000000000000001111"},"finalized_checkpoint":{"epoch":"0","root":"0x0000000000000000000000000000000000000000000000000000000000002222"},"fork_choice_nodes":[{"slot":"32","block_root":"0x0000000000000000000000000000000000000000000000000000000000003333","parent_root":"0x0000000000000000000000000000000000000000000000000000000000004444","justified_epoch":"10","finalized_epoch":"11","weight":"409600000000","validity":"optimistic","execution_block_hash":"0x0000000000000000000000000000000000000000000000000000000000006666","extra_data":{"state_root":"0x0000000000000000000000000000000000000000000000000000000000005555","justified_root":"0x0000000000000000000000000000000000000000000000000000000000007777","unrealised_justified_epoch":"12","unrealized_justified_root":"0x0000000000000000000000000000000000000000000000000000000000009999","unrealised_finalized_epoch":"13","unrealized_finalized_root":"0x0000000000000000000000000000000000000000000000000000000000000000"}}],"extra_data":{}}
\ No newline at end of file
diff --git a/infrastructure/json/src/main/java/tech/pegasys/teku/infrastructure/json/types/DeserializableTypeDefinition.java b/infrastructure/json/src/main/java/tech/pegasys/teku/infrastructure/json/types/DeserializableTypeDefinition.java
index a5b3fe5fef7..79123ba9586 100644
--- a/infrastructure/json/src/main/java/tech/pegasys/teku/infrastructure/json/types/DeserializableTypeDefinition.java
+++ b/infrastructure/json/src/main/java/tech/pegasys/teku/infrastructure/json/types/DeserializableTypeDefinition.java
@@ -60,7 +60,12 @@ static <TKey, TValue> DeserializableTypeDefinition<Map<TKey, TValue>> mapOf(
 
   static <TObject extends Enum<TObject>> EnumTypeDefinition<TObject> enumOf(
       final Class<TObject> itemType) {
-    return new EnumTypeDefinition.EnumTypeBuilder<>(itemType).build();
+    return new EnumTypeDefinition.EnumTypeBuilder<>(itemType, false).build();
+  }
+
+  static <TObject extends Enum<TObject>> EnumTypeDefinition<TObject> enumOf(
+      final Class<TObject> itemType, final boolean forceLowercase) {
+    return new EnumTypeDefinition.EnumTypeBuilder<>(itemType, forceLowercase).build();
   }
 
   static <TObject> DeserializableObjectTypeDefinitionBuilder<TObject, TObject> object(
diff --git a/infrastructure/json/src/main/java/tech/pegasys/teku/infrastructure/json/types/EnumTypeDefinition.java b/infrastructure/json/src/main/java/tech/pegasys/teku/infrastructure/json/types/EnumTypeDefinition.java
index 19c70d500af..b15f5071012 100644
--- a/infrastructure/json/src/main/java/tech/pegasys/teku/infrastructure/json/types/EnumTypeDefinition.java
+++ b/infrastructure/json/src/main/java/tech/pegasys/teku/infrastructure/json/types/EnumTypeDefinition.java
@@ -17,6 +17,7 @@
 import com.fasterxml.jackson.core.JsonParser;
 import java.io.IOException;
 import java.util.HashSet;
+import java.util.Locale;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
@@ -135,8 +136,13 @@ public EnumTypeBuilder(final Class<T> itemType, final Function<T, String> serial
     }
 
     public EnumTypeBuilder(final Class<T> itemType) {
-      this.itemType = itemType;
-      this.serializer = Enum::toString;
+      this(itemType, false);
+    }
+
+    public EnumTypeBuilder(final Class<T> itemType, final boolean forceLowercase) {
+      this(
+          itemType,
+          forceLowercase ? (val) -> val.toString().toLowerCase(Locale.ROOT) : Enum::toString);
     }
 
     public EnumTypeBuilder<T> parser(final Class<T> itemType) {
diff --git a/infrastructure/json/src/test/java/tech/pegasys/teku/infrastructure/json/types/EnumTypeDefinitionTest.java b/infrastructure/json/src/test/java/tech/pegasys/teku/infrastructure/json/types/EnumTypeDefinitionTest.java
index e4085791b08..c241cb810ba 100644
--- a/infrastructure/json/src/test/java/tech/pegasys/teku/infrastructure/json/types/EnumTypeDefinitionTest.java
+++ b/infrastructure/json/src/test/java/tech/pegasys/teku/infrastructure/json/types/EnumTypeDefinitionTest.java
@@ -31,6 +31,18 @@ void shouldSerializeEnum() throws Exception {
     assertThat(json).isEqualTo("\"yes\"");
   }
 
+  @Test
+  void shouldSerializeEnumForceLowerCase() throws Exception {
+    DeserializableTypeDefinition<YES_NO> definition =
+        DeserializableTypeDefinition.enumOf(YES_NO.class);
+    String json = JsonUtil.serialize(YES_NO.YES, definition);
+    assertThat(json).isEqualTo("\"YES\"");
+
+    definition = DeserializableTypeDefinition.enumOf(YES_NO.class, true);
+    json = JsonUtil.serialize(YES_NO.YES, definition);
+    assertThat(json).isEqualTo("\"yes\"");
+  }
+
   @Test
   void shouldParseEnum() throws Exception {
     assertThat(JsonUtil.parse("\"no\"", definition)).isEqualTo(YesNo.NO);
@@ -73,4 +85,10 @@ public String toString() {
       return displayName;
     }
   }
+
+  @SuppressWarnings("JavaCase")
+  private enum YES_NO {
+    YES,
+    NO
+  }
 }