diff --git a/source/vibe/core/sync.d b/source/vibe/core/sync.d
index 7f5edcc..aaf298f 100644
--- a/source/vibe/core/sync.d
+++ b/source/vibe/core/sync.d
@@ -716,6 +716,7 @@ struct LocalManualEvent {
 	/// Emits the signal, waking up all owners of the signal.
 	int emit()
 	nothrow {
+		assert(m_waiter !is null, "LocalManualEvent is not initialized - use createManualEvent()");
 		logTrace("unshared emit");
 		auto ec = m_waiter.m_emitCount++;
 		m_waiter.emit();
@@ -725,6 +726,7 @@ struct LocalManualEvent {
 	/// Emits the signal, waking up a single owners of the signal.
 	int emitSingle()
 	nothrow {
+		assert(m_waiter !is null, "LocalManualEvent is not initialized - use createManualEvent()");
 		logTrace("unshared single emit");
 		auto ec = m_waiter.m_emitCount++;
 		m_waiter.emitSingle();
@@ -768,6 +770,8 @@ struct LocalManualEvent {
 	{
 		import std.datetime : Clock, SysTime, UTC;
 
+		assert(m_waiter !is null, "LocalManualEvent is not initialized - use createManualEvent()");
+
 		SysTime target_timeout, now;
 		if (timeout != Duration.max) {
 			try now = Clock.currTime(UTC());