diff --git a/src/main/java/li/cil/oc2/common/bus/AbstractDeviceBusElement.java b/src/main/java/li/cil/oc2/common/bus/AbstractDeviceBusElement.java
index a22bfe20..60129a67 100644
--- a/src/main/java/li/cil/oc2/common/bus/AbstractDeviceBusElement.java
+++ b/src/main/java/li/cil/oc2/common/bus/AbstractDeviceBusElement.java
@@ -35,7 +35,7 @@ public abstract class AbstractDeviceBusElement implements DeviceBusElement {
 
     @Override
     public Collection<DeviceBusController> getControllers() {
-        return controllers;
+        return Collections.unmodifiableSet(controllers);
     }
 
     @Override