What causes "A receiver method must not be static: " in quarkusio/quarkus?

Remove the `static` modifier from the receiver method.

quarkusio/quarkus · error · IllegalStateException

A receiver method must not be static:

Error message

A receiver method must not be static:

What it means

The Quarkus signals extension builds invokers for receiver methods (methods annotated to receive signals). A receiver method must be an instance method because the bean instance is used as the receiver target; a static method has no instance to invoke against. During discovery of receivers, a static method is rejected with this IllegalStateException.

Source

Thrown at extensions/signals/deployment/src/main/java/io/quarkus/signals/deployment/SignalsProcessor.java:153

                                    throw new IllegalStateException(
                                            "A receiver method must have exactly one parameter annotated with @Receives: "
                                                    + methodDesc(method));
                                }
                                signalParam = param;
                            }
                        }
                    }
                    if (!seenMethods.add(method.signatureKey())) {
                        // Overridden by a subclass
                        continue;
                    }
                    if (signalParam != null) {
                        if (Modifier.isPrivate(method.flags())) {
                            throw new IllegalStateException(
                                    "A receiver method must not be private: " + methodDesc(method));
                        }
                        if (Modifier.isStatic(method.flags())) {
                            throw new IllegalStateException(
                                    "A receiver method must not be static: " + methodDesc(method));
                        }
                        ExecutionModel executionModel = getExecutionModel(method);
                        if (!receiverExecutorImplementation.isSupported(executionModel)) {
                            throw new IllegalStateException(
                                    "%s execution model is not supported: %s".formatted(executionModel, methodDesc(method)));
                        }
                        InvokerBuilder invokerBuilder = invokerFactory.createInvoker(bean, method)
                                .withInstanceLookup();
                        if (params.size() > 1) {
                            for (MethodParameterInfo param : params) {
                                if (param != signalParam) {
                                    invokerBuilder.withArgumentLookup(param.position());
                                }
                            }
                        }
                        List<AnnotationInstance> qualifiers = new ArrayList<>();
                        for (AnnotationInstance a : signalParam.declaredAnnotations()) {

View on GitHub (pinned to e1c734241f)

Solutions

Remove the `static` modifier from the receiver method.
Ensure the method is on a CDI bean instance so the generated invoker can call it on the bean.
If the method was never intended to receive signals, remove the signal annotation/parameter so it is not discovered as a receiver.

Example fix

// before
@SignalReceiver
static void onSig(SignalEvent evt) { ... }

// after
@SignalReceiver
void onSig(SignalEvent evt) { ... }

Defensive patterns

Strategy: validation

Validate before calling

if (java.lang.reflect.Modifier.isStatic(ReceiverClass.class.getDeclaredMethod("onSig", SignalEvent.class).getModifiers())) { throw new IllegalStateException("receiver method must not be static"); }

Prevention

Never mark signal receiver methods static.
Keep receiver methods on managed CDI bean classes.
Review refactors that add `static` to instance handler methods.

When it happens

Trigger: Declaring a signal receiver method as `static` (e.g. `static void onSignal(...)` with a signal parameter) in a bean discovered by the signals processor.

Common situations: Developers copying a listener style from plain-Java signal handling where static handlers are common, or making a helper method static after refactoring.

Related errors

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/cd9e0cd33338e249. Report an issue: GitHub.