diff --git a/wire-kotlin-generator/api/wire-kotlin-generator.api b/wire-kotlin-generator/api/wire-kotlin-generator.api
index a10f6bc8c5..5357198de6 100644
--- a/wire-kotlin-generator/api/wire-kotlin-generator.api
+++ b/wire-kotlin-generator/api/wire-kotlin-generator.api
@@ -1,6 +1,6 @@
 public final class com/squareup/wire/kotlin/KotlinGenerator {
 	public static final field Companion Lcom/squareup/wire/kotlin/KotlinGenerator$Companion;
-	public synthetic fun <init> (Lcom/squareup/wire/schema/Schema;Ljava/util/Map;Ljava/util/Map;Lcom/squareup/wire/schema/Profile;ZZZZLcom/squareup/wire/kotlin/RpcCallStyle;Lcom/squareup/wire/kotlin/RpcRole;ILjava/lang/String;ZZLkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public synthetic fun <init> (Lcom/squareup/wire/schema/Schema;Ljava/util/Map;Ljava/util/Map;Lcom/squareup/wire/schema/Profile;ZZZZLcom/squareup/wire/kotlin/RpcCallStyle;Lcom/squareup/wire/kotlin/RpcRole;ILjava/lang/String;ZZZLkotlin/jvm/internal/DefaultConstructorMarker;)V
 	public final fun generateOptionType (Lcom/squareup/wire/schema/Extend;Lcom/squareup/wire/schema/Field;)Lcom/squareup/kotlinpoet/TypeSpec;
 	public final fun generateServiceTypeSpecs (Lcom/squareup/wire/schema/Service;Lcom/squareup/wire/schema/Rpc;)Ljava/util/Map;
 	public static synthetic fun generateServiceTypeSpecs$default (Lcom/squareup/wire/kotlin/KotlinGenerator;Lcom/squareup/wire/schema/Service;Lcom/squareup/wire/schema/Rpc;ILjava/lang/Object;)Ljava/util/Map;
@@ -9,14 +9,14 @@ public final class com/squareup/wire/kotlin/KotlinGenerator {
 	public static synthetic fun generatedServiceName$default (Lcom/squareup/wire/kotlin/KotlinGenerator;Lcom/squareup/wire/schema/Service;Lcom/squareup/wire/schema/Rpc;ZILjava/lang/Object;)Lcom/squareup/kotlinpoet/ClassName;
 	public final fun generatedTypeName (Lcom/squareup/wire/schema/ProtoMember;)Lcom/squareup/kotlinpoet/ClassName;
 	public final fun generatedTypeName (Lcom/squareup/wire/schema/Type;)Lcom/squareup/kotlinpoet/ClassName;
-	public static final fun get (Lcom/squareup/wire/schema/Schema;Lcom/squareup/wire/schema/Profile;ZZZZLcom/squareup/wire/kotlin/RpcCallStyle;Lcom/squareup/wire/kotlin/RpcRole;ILjava/lang/String;ZZ)Lcom/squareup/wire/kotlin/KotlinGenerator;
+	public static final fun get (Lcom/squareup/wire/schema/Schema;Lcom/squareup/wire/schema/Profile;ZZZZLcom/squareup/wire/kotlin/RpcCallStyle;Lcom/squareup/wire/kotlin/RpcRole;ILjava/lang/String;ZZZ)Lcom/squareup/wire/kotlin/KotlinGenerator;
 	public final fun getSchema ()Lcom/squareup/wire/schema/Schema;
 }
 
 public final class com/squareup/wire/kotlin/KotlinGenerator$Companion {
 	public final fun builtInType (Lcom/squareup/wire/schema/ProtoType;)Z
-	public final fun get (Lcom/squareup/wire/schema/Schema;Lcom/squareup/wire/schema/Profile;ZZZZLcom/squareup/wire/kotlin/RpcCallStyle;Lcom/squareup/wire/kotlin/RpcRole;ILjava/lang/String;ZZ)Lcom/squareup/wire/kotlin/KotlinGenerator;
-	public static synthetic fun get$default (Lcom/squareup/wire/kotlin/KotlinGenerator$Companion;Lcom/squareup/wire/schema/Schema;Lcom/squareup/wire/schema/Profile;ZZZZLcom/squareup/wire/kotlin/RpcCallStyle;Lcom/squareup/wire/kotlin/RpcRole;ILjava/lang/String;ZZILjava/lang/Object;)Lcom/squareup/wire/kotlin/KotlinGenerator;
+	public final fun get (Lcom/squareup/wire/schema/Schema;Lcom/squareup/wire/schema/Profile;ZZZZLcom/squareup/wire/kotlin/RpcCallStyle;Lcom/squareup/wire/kotlin/RpcRole;ILjava/lang/String;ZZZ)Lcom/squareup/wire/kotlin/KotlinGenerator;
+	public static synthetic fun get$default (Lcom/squareup/wire/kotlin/KotlinGenerator$Companion;Lcom/squareup/wire/schema/Schema;Lcom/squareup/wire/schema/Profile;ZZZZLcom/squareup/wire/kotlin/RpcCallStyle;Lcom/squareup/wire/kotlin/RpcRole;ILjava/lang/String;ZZZILjava/lang/Object;)Lcom/squareup/wire/kotlin/KotlinGenerator;
 }
 
 public final class com/squareup/wire/kotlin/KotlinSchemaHandler : com/squareup/wire/schema/SchemaHandler {
diff --git a/wire-kotlin-generator/src/main/java/com/squareup/wire/kotlin/KotlinGenerator.kt b/wire-kotlin-generator/src/main/java/com/squareup/wire/kotlin/KotlinGenerator.kt
index 54b90fe019..366b8be857 100644
--- a/wire-kotlin-generator/src/main/java/com/squareup/wire/kotlin/KotlinGenerator.kt
+++ b/wire-kotlin-generator/src/main/java/com/squareup/wire/kotlin/KotlinGenerator.kt
@@ -129,6 +129,11 @@ class KotlinGenerator private constructor(
   private val nameSuffix: String?,
   private val buildersOnly: Boolean,
   private val escapeKotlinKeywords: Boolean,
+  /**
+   * If true, generated enums will have an extra `UNRECOGNIZED` constant with a value of `-1`. This
+   * only applies to enum which syntax is proto3.
+   */
+  private val generateUnrecognizedEnumConstant: Boolean,
 ) {
   private val nameAllocatorStore = mutableMapOf<Type, NameAllocator>()
 
@@ -2214,6 +2219,25 @@ class KotlinGenerator private constructor(
    * }
    */
   private fun generateEnum(enum: EnumType): TypeSpec {
+    @Suppress("NAME_SHADOWING")
+    val enum =
+      if (enum.syntax == Syntax.PROTO_3 && generateUnrecognizedEnumConstant) {
+        // We mutate the constant by inserting `UNRECOGNIZED(-1)` at the front of the list.
+        enum.copy(
+          constants = listOf(
+            EnumConstant(
+              location = enum.location,
+              name = "UNRECOGNIZED",
+              tag = -1,
+              documentation = "",
+              options = Options(optionType = ENUM_OPTIONS, optionElements = listOf()),
+            ),
+          ) + enum.constants,
+        )
+      } else {
+        enum
+      }
+
     val type = enum.type
     val nameAllocator = nameAllocator(enum)
 
@@ -2886,6 +2910,7 @@ class KotlinGenerator private constructor(
       nameSuffix: String? = null,
       buildersOnly: Boolean = false,
       escapeKotlinKeywords: Boolean = false,
+      generateUnrecognizedEnumConstant: Boolean = false,
     ): KotlinGenerator {
       val typeToKotlinName = mutableMapOf<ProtoType, TypeName>()
       val memberToKotlinName = mutableMapOf<ProtoMember, TypeName>()
@@ -2934,6 +2959,7 @@ class KotlinGenerator private constructor(
         nameSuffix = nameSuffix,
         buildersOnly = buildersOnly,
         escapeKotlinKeywords = escapeKotlinKeywords,
+        generateUnrecognizedEnumConstant = generateUnrecognizedEnumConstant,
       )
     }
 
diff --git a/wire-kotlin-generator/src/test/java/com/squareup/wire/kotlin/KotlinGeneratorTest.kt b/wire-kotlin-generator/src/test/java/com/squareup/wire/kotlin/KotlinGeneratorTest.kt
index e6212fc2c4..69d8f9f3ed 100644
--- a/wire-kotlin-generator/src/test/java/com/squareup/wire/kotlin/KotlinGeneratorTest.kt
+++ b/wire-kotlin-generator/src/test/java/com/squareup/wire/kotlin/KotlinGeneratorTest.kt
@@ -66,6 +66,50 @@ class KotlinGeneratorTest {
     assertThat(code).contains("WORK(1),")
   }
 
+  @Test fun generateUnrecognizedEnumConstantIsIgnoredForProto2() {
+    val schema = buildSchema {
+      add(
+        "message.proto".toPath(),
+        """
+        |syntax = "proto2";
+        |enum PhoneType {
+        |	HOME = 0;
+        |	WORK = 1;
+        |	MOBILE = 2;
+        |}
+        """.trimMargin(),
+      )
+    }
+    val code = KotlinWithProfilesGenerator(schema)
+      .generateKotlin("PhoneType", generateUnrecognizedEnumConstant = true)
+    assertThat(code).contains("HOME(0),")
+    assertThat(code).contains("WORK(1),")
+    assertThat(code).contains("MOBILE(2),")
+    assertThat(code).doesNotContain("UNRECOGNIZED(-1),")
+  }
+
+  @Test fun generateUnrecognizedEnumConstantIsAppliedForProto3() {
+    val schema = buildSchema {
+      add(
+        "message.proto".toPath(),
+        """
+        |syntax = "proto3";
+        |enum PhoneType {
+        |	HOME = 0;
+        |	WORK = 1;
+        |	MOBILE = 2;
+        |}
+        """.trimMargin(),
+      )
+    }
+    val code = KotlinWithProfilesGenerator(schema)
+      .generateKotlin("PhoneType", generateUnrecognizedEnumConstant = true)
+    assertThat(code).contains("HOME(0),")
+    assertThat(code).contains("WORK(1),")
+    assertThat(code).contains("MOBILE(2),")
+    assertThat(code).contains("UNRECOGNIZED(-1),")
+  }
+
   @Test fun defaultValues() {
     val schema = buildSchema {
       add(
diff --git a/wire-kotlin-generator/src/test/java/com/squareup/wire/kotlin/KotlinWithProfilesGenerator.kt b/wire-kotlin-generator/src/test/java/com/squareup/wire/kotlin/KotlinWithProfilesGenerator.kt
index 838138c59b..5d08101489 100644
--- a/wire-kotlin-generator/src/test/java/com/squareup/wire/kotlin/KotlinWithProfilesGenerator.kt
+++ b/wire-kotlin-generator/src/test/java/com/squareup/wire/kotlin/KotlinWithProfilesGenerator.kt
@@ -52,6 +52,7 @@ internal class KotlinWithProfilesGenerator(private val schema: Schema) {
     boxOneOfsMinSize: Int = 5_000,
     buildersOnly: Boolean = false,
     javaInterop: Boolean = false,
+    generateUnrecognizedEnumConstant: Boolean = false,
   ): String {
     val kotlinGenerator = KotlinGenerator(
       schema,
@@ -59,6 +60,7 @@ internal class KotlinWithProfilesGenerator(private val schema: Schema) {
       boxOneOfsMinSize = boxOneOfsMinSize,
       buildersOnly = buildersOnly,
       javaInterop = javaInterop,
+      generateUnrecognizedEnumConstant = generateUnrecognizedEnumConstant,
     )
     val type = schema.getType(typeName)!!
     val typeSpec = kotlinGenerator.generateType(type)