diff --git a/src/main/java/net/minecraftforge/fml/CrashReportExtender.java b/src/main/java/net/minecraftforge/fml/CrashReportExtender.java
index 41ba3f694..f94301a5d 100644
--- a/src/main/java/net/minecraftforge/fml/CrashReportExtender.java
+++ b/src/main/java/net/minecraftforge/fml/CrashReportExtender.java
@@ -25,12 +25,13 @@ import net.minecraft.crash.CrashReportCategory;
 import net.minecraftforge.fml.common.ICrashCallable;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.Callable;
 
 public class CrashReportExtender
 {
-    private static List<ICrashCallable> crashCallables = new ArrayList<>();
+    private static List<ICrashCallable> crashCallables = Collections.synchronizedList(new ArrayList<>());
 
     public static void enhanceCrashReport(final CrashReport crashReport, final CrashReportCategory category)
     {
diff --git a/src/main/java/net/minecraftforge/fml/network/FMLMCRegisterPacketHandler.java b/src/main/java/net/minecraftforge/fml/network/FMLMCRegisterPacketHandler.java
index 16f2cdb1a..2d83fc286 100644
--- a/src/main/java/net/minecraftforge/fml/network/FMLMCRegisterPacketHandler.java
+++ b/src/main/java/net/minecraftforge/fml/network/FMLMCRegisterPacketHandler.java
@@ -32,7 +32,9 @@ import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.util.HashSet;
+import java.util.Optional;
 import java.util.Set;
+import java.util.function.Supplier;
 
 public class FMLMCRegisterPacketHandler {
     public static final FMLMCRegisterPacketHandler INSTANCE = new FMLMCRegisterPacketHandler();
@@ -40,10 +42,18 @@ public class FMLMCRegisterPacketHandler {
     public static class ChannelList {
         private Set<ResourceLocation> locations = new HashSet<>();
 
-        public void updateFrom(PacketBuffer buffer) {
-            byte[] data = new byte[buffer.readableBytes() < 0 ? 0 : buffer.readableBytes()];
+        public void updateFrom(final Supplier<NetworkEvent.Context> source, PacketBuffer buffer, final NetworkEvent.RegistrationChangeType changeType) {
+            byte[] data = new byte[Math.max(buffer.readableBytes(), 0)];
             buffer.readBytes(data);
-            locations = bytesToResLocation(data);
+            Set<ResourceLocation> oldLocations = this.locations;
+            this.locations = bytesToResLocation(data);
+            // ensure all locations receive updates, old and new.
+            oldLocations.addAll(this.locations);
+            oldLocations.stream()
+                    .map(NetworkRegistry::findTarget)
+                    .filter(Optional::isPresent)
+                    .map(Optional::get)
+                    .forEach(t->t.dispatchEvent(new NetworkEvent.ChannelRegistrationChangeEvent(source, changeType)));
         }
 
         byte[] toByteArray() {
@@ -79,13 +89,13 @@ public class FMLMCRegisterPacketHandler {
 
     void registerListener(NetworkEvent evt) {
         final ChannelList channelList = getFrom(evt);
-        channelList.updateFrom(evt.getPayload());
+        channelList.updateFrom(evt.getSource(), evt.getPayload(), NetworkEvent.RegistrationChangeType.REGISTER);
         evt.getSource().get().setPacketHandled(true);
     }
 
     void unregisterListener(NetworkEvent evt) {
         final ChannelList channelList = getFrom(evt);
-        channelList.updateFrom(evt.getPayload());
+        channelList.updateFrom(evt.getSource(), evt.getPayload(), NetworkEvent.RegistrationChangeType.UNREGISTER);
         evt.getSource().get().setPacketHandled(true);
     }
 
diff --git a/src/main/java/net/minecraftforge/fml/network/NetworkEvent.java b/src/main/java/net/minecraftforge/fml/network/NetworkEvent.java
index a50a0435c..170e7bab9 100644
--- a/src/main/java/net/minecraftforge/fml/network/NetworkEvent.java
+++ b/src/main/java/net/minecraftforge/fml/network/NetworkEvent.java
@@ -58,6 +58,12 @@ public class NetworkEvent extends Event
         this.loginIndex = loginIndex;
     }
 
+    public NetworkEvent(final Supplier<Context> source) {
+        this.source = source;
+        this.payload = null;
+        this.loginIndex = -1;
+    }
+
     public PacketBuffer getPayload()
     {
         return payload;
@@ -122,6 +128,30 @@ public class NetworkEvent extends Event
             super(payload, source, loginIndex);
         }
     }
+
+    public enum RegistrationChangeType {
+        REGISTER, UNREGISTER;
+    }
+
+    /**
+     * Fired when the channel registration (see minecraft custom channel documentation) changes. Note the payload
+     * is not exposed. This fires to the resource location that owns the channel, when it's registration changes state.
+     *
+     * It seems plausible that this will fire multiple times for the same state, depending on what the server is doing.
+     * It just directly dispatches upon receipt.
+     */
+    public static class ChannelRegistrationChangeEvent extends NetworkEvent {
+        private final RegistrationChangeType changeType;
+
+        ChannelRegistrationChangeEvent(final Supplier<Context> source, RegistrationChangeType changeType) {
+            super(source);
+            this.changeType = changeType;
+        }
+
+        public RegistrationChangeType getRegistrationChangeType() {
+            return this.changeType;
+        }
+    }
     /**
      * Context for {@link NetworkEvent}
      */
diff --git a/src/main/java/net/minecraftforge/fml/network/NetworkInstance.java b/src/main/java/net/minecraftforge/fml/network/NetworkInstance.java
index 38456d1bb..7999a96df 100644
--- a/src/main/java/net/minecraftforge/fml/network/NetworkInstance.java
+++ b/src/main/java/net/minecraftforge/fml/network/NetworkInstance.java
@@ -25,9 +25,11 @@ import net.minecraftforge.eventbus.api.BusBuilder;
 import net.minecraftforge.eventbus.api.Event;
 import net.minecraftforge.eventbus.api.IEventBus;
 import net.minecraftforge.eventbus.api.IEventListener;
+import net.minecraftforge.fml.network.simple.SimpleChannel;
 
 import java.util.List;
 import java.util.function.Consumer;
+import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.function.Supplier;
 
@@ -83,7 +85,6 @@ public class NetworkInstance
         return context.getPacketHandled();
     }
 
-
     String getNetworkProtocolVersion() {
         return networkProtocolVersion;
     }
@@ -103,4 +104,8 @@ public class NetworkInstance
     void dispatchLoginPacket(final NetworkEvent.LoginPayloadEvent loginPayloadEvent) {
         this.networkEventBus.post(loginPayloadEvent);
     }
+
+    void dispatchEvent(final NetworkEvent networkEvent) {
+        this.networkEventBus.post(networkEvent);
+    }
 }