diff --git a/protos/generate-protos.sh b/protos/generate-protos.sh
index 48ed3f3e..fd0dbb12 100755
--- a/protos/generate-protos.sh
+++ b/protos/generate-protos.sh
@@ -4,6 +4,8 @@
 
 protoc gtfs-realtime.proto --java_out=../src/main/java/
 
+protoc gtfs-realtime-extension.proto --java_out=../src/main/java/
+
 protoc pubtrans-tables.proto --java_out=../src/main/java/
 
 protoc internal-messages.proto --java_out=../src/main/java/
@@ -17,3 +19,4 @@ protoc metro-ats.proto --java_out=../src/main/java/
 protoc passenger-count.proto --java_out=../src/main/java/
 
 protoc eke.proto --java_out=../src/main/java/
+
diff --git a/protos/gtfs-realtime-extension.proto b/protos/gtfs-realtime-extension.proto
new file mode 100644
index 00000000..a8a84cc4
--- /dev/null
+++ b/protos/gtfs-realtime-extension.proto
@@ -0,0 +1,11 @@
+syntax = "proto2";
+package proto;
+
+option java_package = "fi.hsl.common.gtfsrt.proto";
+option java_outer_classname = "AlternativeStops";
+
+import public "gtfs-realtime.proto";
+
+extend transit_realtime.TripUpdate.StopTimeUpdate {
+    repeated string alternative_stop_ids = 1999;
+}
\ No newline at end of file
diff --git a/src/main/java/fi/hsl/common/gtfsrt/proto/AlternativeStops.java b/src/main/java/fi/hsl/common/gtfsrt/proto/AlternativeStops.java
new file mode 100644
index 00000000..239d9126
--- /dev/null
+++ b/src/main/java/fi/hsl/common/gtfsrt/proto/AlternativeStops.java
@@ -0,0 +1,54 @@
+// Generated by the protocol buffer compiler.  DO NOT EDIT!
+// source: gtfs-realtime-extension.proto
+
+package fi.hsl.common.gtfsrt.proto;
+
+public final class AlternativeStops {
+  private AlternativeStops() {}
+  public static void registerAllExtensions(
+      com.google.protobuf.ExtensionRegistryLite registry) {
+    registry.add(fi.hsl.common.gtfsrt.proto.AlternativeStops.alternativeStopIds);
+  }
+
+  public static void registerAllExtensions(
+      com.google.protobuf.ExtensionRegistry registry) {
+    registerAllExtensions(
+        (com.google.protobuf.ExtensionRegistryLite) registry);
+  }
+  public static final int ALTERNATIVE_STOP_IDS_FIELD_NUMBER = 1999;
+  /**
+   * <code>extend .transit_realtime.TripUpdate.StopTimeUpdate { ... }</code>
+   */
+  public static final
+    com.google.protobuf.GeneratedMessage.GeneratedExtension<
+      com.google.transit.realtime.GtfsRealtime.TripUpdate.StopTimeUpdate,
+      java.util.List<java.lang.String>> alternativeStopIds = com.google.protobuf.GeneratedMessage
+          .newFileScopedGeneratedExtension(
+        java.lang.String.class,
+        null);
+
+  public static com.google.protobuf.Descriptors.FileDescriptor
+      getDescriptor() {
+    return descriptor;
+  }
+  private static  com.google.protobuf.Descriptors.FileDescriptor
+      descriptor;
+  static {
+    java.lang.String[] descriptorData = {
+      "\n\035gtfs-realtime-extension.proto\022\005proto\032\023" +
+      "gtfs-realtime.proto:J\n\024alternative_stop_" +
+      "ids\022+.transit_realtime.TripUpdate.StopTi" +
+      "meUpdate\030\317\017 \003(\tB.\n\032fi.hsl.common.gtfsrt." +
+      "protoB\020AlternativeStopsP\000"
+    };
+    descriptor = com.google.protobuf.Descriptors.FileDescriptor
+      .internalBuildGeneratedFileFrom(descriptorData,
+        new com.google.protobuf.Descriptors.FileDescriptor[] {
+          com.google.transit.realtime.GtfsRealtime.getDescriptor(),
+        });
+    alternativeStopIds.internalInit(descriptor.getExtensions().get(0));
+    com.google.transit.realtime.GtfsRealtime.getDescriptor();
+  }
+
+  // @@protoc_insertion_point(outer_class_scope)
+}