diff --git a/protobuf/protobuf-api/build.gradle.kts b/protobuf/protobuf-api/build.gradle.kts
index ac453aee0..8d5221f1b 100644
--- a/protobuf/protobuf-api/build.gradle.kts
+++ b/protobuf/protobuf-api/build.gradle.kts
@@ -32,6 +32,7 @@ kotlin {
 
         commonTest {
             dependencies {
+                implementation(projects.protobuf.protobufWkt)
                 implementation(libs.kotlin.test)
                 implementation(libs.coroutines.test)
             }
diff --git a/protobuf/protobuf-api/src/commonTest/kotlin/kotlinx/rpc/protobuf/test/ProtosTest.kt b/protobuf/protobuf-api/src/commonTest/kotlin/kotlinx/rpc/protobuf/test/ProtosTest.kt
index bddf90ff9..fff541638 100644
--- a/protobuf/protobuf-api/src/commonTest/kotlin/kotlinx/rpc/protobuf/test/ProtosTest.kt
+++ b/protobuf/protobuf-api/src/commonTest/kotlin/kotlinx/rpc/protobuf/test/ProtosTest.kt
@@ -446,4 +446,14 @@ class ProtosTest {
             (decoded.oneOfWithGroup as WithGroups.OneOfWithGroup.Testgroup).value.value
         )
     }
+
+    @Test
+    fun testGroupAsStandalone() {
+        val standaloneGroup = WithGroups.FirstGroup {
+            value = 42u
+        }
+
+        val decoded = encodeDecode(standaloneGroup, marshallerOf<WithGroups.FirstGroup>())
+        assertEquals(standaloneGroup.value, decoded.value)
+    }
 }
diff --git a/protoc-gen/protobuf/src/main/kotlin/kotlinx/rpc/protoc/gen/ModelToProtobufKotlinCommonGenerator.kt b/protoc-gen/protobuf/src/main/kotlin/kotlinx/rpc/protoc/gen/ModelToProtobufKotlinCommonGenerator.kt
index 9fa64f94e..39e378d1a 100644
--- a/protoc-gen/protobuf/src/main/kotlin/kotlinx/rpc/protoc/gen/ModelToProtobufKotlinCommonGenerator.kt
+++ b/protoc-gen/protobuf/src/main/kotlin/kotlinx/rpc/protoc/gen/ModelToProtobufKotlinCommonGenerator.kt
@@ -101,12 +101,9 @@ class ModelToProtobufKotlinCommonGenerator(
     private fun CodeGenerator.generatePublicMessage(declaration: MessageDeclaration) {
         if (!declaration.isUserFacing) return
 
-        val annotations = mutableListOf<ScopedFormattedString>()
-        if (!declaration.isGroup) {
-            annotations.add(
-                FqName.Annotations.GeneratedProtoMessage.scopedAnnotation()
-            )
-        }
+        val annotations = listOf(
+            FqName.Annotations.GeneratedProtoMessage.scopedAnnotation()
+        )
 
         generatedMetadata.protoNamesList.add(declaration.name)
 
@@ -773,8 +770,6 @@ class ModelToProtobufKotlinCommonGenerator(
 
     private fun CodeGenerator.generateMarshallerObject(declaration: MessageDeclaration) {
         if (!declaration.isUserFacing) return
-        // the MARSHALLER object is not necessary for groups, as they are inlined messages
-        if (declaration.isGroup) return
 
         clazz(
             name = declaration.marshallerObjectName.simpleName,
@@ -808,8 +803,11 @@ class ModelToProtobufKotlinCommonGenerator(
                 scope("%T(source).use".scoped(FqName.RpcClasses.WireDecoder)) {
                     code("val msg = %T()".scoped(declaration.internalClassName))
                     scope("checkForPlatformDecodeException".scoped(), nlAfterClosed = false) {
+                        // if the message declaration is a group, we must pass null as the
+                        // startGroup tag to indicate that this message is decoded as standalone (like a normal message)
+                        val groupExtraArg = if (declaration.isGroup) ", null" else ""
                         code(
-                            "%T.decodeWith(msg, it, config as? %T)".scoped(
+                            "%T.decodeWith(msg, it, config as? %T$groupExtraArg)".scoped(
                                 declaration.internalClassName,
                                 FqName.RpcClasses.ProtobufConfig,
                             )
@@ -828,7 +826,6 @@ class ModelToProtobufKotlinCommonGenerator(
 
     private fun CodeGenerator.generateDescriptorObject(declaration: MessageDeclaration) {
         if (!declaration.isUserFacing) return
-        if (declaration.isGroup) return
 
         clazz(
             name = "DESCRIPTOR",
@@ -881,8 +878,12 @@ class ModelToProtobufKotlinCommonGenerator(
             .scoped(declaration.internalClassName, FqName.RpcClasses.WireDecoder, FqName.RpcClasses.ProtobufConfig)
 
         if (declaration.isGroup) {
+            // if the message is a group message, the decoder accepts an optional startGroup tag, which indicates
+            // that the decoding of the message must end with an END_GROUP tag of the same fieldNr.
+            // if the startGroup tag is null, we treat it like a normal message.
+            // the argument is not default null, to avoid that we forget to set it when changing the generator.
             args = args.merge(FqName.RpcClasses.KTag.scoped()) { start, kTag ->
-                "$start, startGroup: $kTag"
+                "$start, startGroup: $kTag?"
             }
         }
 
@@ -895,14 +896,21 @@ class ModelToProtobufKotlinCommonGenerator(
         ) {
             whileBlock("true".scoped()) {
                 if (declaration.isGroup) {
-                    code(
-                        "val tag = decoder.readTag() ?: throw %T(\"Missing END_GROUP tag for field: \${startGroup.fieldNr}.\")"
-                            .scoped(FqName.RpcClasses.ProtobufDecodingException)
-                    )
+                    scope("val tag = decoder.readTag() ?: run".scoped()) {
+                        // if the startGroup tag is set, we decode the message as an inline group message,
+                        // so in case of the tag being null, we know that the payload is malformed
+                        scope("startGroup?.let".scoped()) {
+                            code("throw %T(\"Missing END_GROUP tag for field: \${startGroup.fieldNr}.\")"
+                                .scoped(FqName.RpcClasses.ProtobufDecodingException))
+                        }
+                        // if the startGroup is null, we decode the message like a normal non-group message,
+                        // so we stop when the tag is null
+                        code("return".scoped())
+                    }
                     ifBranch(condition = "tag.wireType == %T".scoped(FqName.RpcClasses.WireType_END_GROUP), ifBlock = {
-                        ifBranch(condition = "tag.fieldNr != startGroup.fieldNr".scoped(), ifBlock = {
+                        ifBranch(condition = "tag.fieldNr != startGroup?.fieldNr".scoped(), ifBlock = {
                             code(
-                                "throw %T(\"Wrong END_GROUP tag. Expected \${startGroup.fieldNr}, got \${tag.fieldNr}.\")"
+                                "throw %T(\"Wrong END_GROUP tag. Expected \${startGroup?.fieldNr}, got \${tag.fieldNr}.\")"
                                     .scoped(FqName.RpcClasses.ProtobufDecodingException)
                             )
                         })