diff --git a/concurrentutil/src/main/java/ca/spottedleaf/concurrentutil/scheduler/EDFSchedulerThreadPool.java b/concurrentutil/src/main/java/ca/spottedleaf/concurrentutil/scheduler/EDFSchedulerThreadPool.java
index b66b1c7..f787b32 100644
--- a/concurrentutil/src/main/java/ca/spottedleaf/concurrentutil/scheduler/EDFSchedulerThreadPool.java
+++ b/concurrentutil/src/main/java/ca/spottedleaf/concurrentutil/scheduler/EDFSchedulerThreadPool.java
@@ -226,6 +226,10 @@ private ScheduledState returnTask(final TickThreadRunner runner, final Scheduled
     @Override
     public void schedule(final SchedulableTick task) {
         synchronized (this.scheduleLock) {
+            if (task.getScheduledStart() == TimeUtil.DEADLINE_NOT_SET) {
+                throw new IllegalStateException("Start must be set when scheduling");
+            }
+
             final ScheduledState state = new ScheduledState(task);
             if (!task.setState(state)) {
                 throw new IllegalStateException("Task " + task + " is already scheduled or cancelled");
@@ -284,17 +288,17 @@ public boolean updateTickStartToMax(final ScheduledState task, final long newSta
 
     @Override
     public boolean cancel(final SchedulableTick task) {
-        if (!(task.state instanceof ScheduledState state)) {
-            return false;
-        }
-
-        if (state.schedulerOwnedBy != this) {
+        if (!(task.getState() instanceof ScheduledState state)) {
             return false;
         }
 
         synchronized (this.scheduleLock) {
+            if (state.schedulerOwnedBy != this) {
+                return false;
+            }
             if (this.queued.remove(state)) {
                 // cancelled, and no runner owns it - so return
+                state.tryMarkCancelled();
                 return true;
             }
             if (state.awaitingLink != null) {
@@ -312,10 +316,16 @@ public boolean cancel(final SchedulableTick task) {
                     runner.replaceTask(replace);
                 }
 
+                state.tryMarkCancelled();
                 return true;
             }
 
-            // could not find it in queue
+            if (state.ownedBy != null) {
+                // the runner is currently executing the tick, it will not reschedule the task if cancelled
+                return state.tryMarkCancelled();
+            }
+
+            // not queued, not awaiting, and not owned by a runner - the task has completed or is already cancelled
             return false;
         }
     }
diff --git a/concurrentutil/src/main/java/ca/spottedleaf/concurrentutil/scheduler/SchedulableTick.java b/concurrentutil/src/main/java/ca/spottedleaf/concurrentutil/scheduler/SchedulableTick.java
index fa594cb..dd477ac 100644
--- a/concurrentutil/src/main/java/ca/spottedleaf/concurrentutil/scheduler/SchedulableTick.java
+++ b/concurrentutil/src/main/java/ca/spottedleaf/concurrentutil/scheduler/SchedulableTick.java
@@ -32,7 +32,11 @@ public abstract class SchedulableTick {
 
     long scheduledStart = TimeUtil.DEADLINE_NOT_SET;
 
-    Object state;
+    private volatile Object state;
+
+    final Object getState() {
+        return this.state;
+    }
 
     boolean setState(final Object state) {
         synchronized (this) {
@@ -79,7 +83,7 @@ protected final void setScheduledStart(final long value) {
     public String toString() {
         return "SchedulableTick:{" +
                 "class=" + this.getClass().getName() + "," +
-                "state=" + this.state + ","
+                "state=" + this.getState() + ","
                 + "}";
     }
 }
diff --git a/concurrentutil/src/main/java/ca/spottedleaf/concurrentutil/scheduler/StealingScheduledThreadPool.java b/concurrentutil/src/main/java/ca/spottedleaf/concurrentutil/scheduler/StealingScheduledThreadPool.java
index a4ce487..0729685 100644
--- a/concurrentutil/src/main/java/ca/spottedleaf/concurrentutil/scheduler/StealingScheduledThreadPool.java
+++ b/concurrentutil/src/main/java/ca/spottedleaf/concurrentutil/scheduler/StealingScheduledThreadPool.java
@@ -68,7 +68,7 @@ public OSNuma getNuma() {
     }
 
     private static ScheduledState getState(final SchedulableTick tick) {
-        return (ScheduledState)tick.state;
+        return (ScheduledState)tick.getState();
     }
 
     private static Thread[] getThreads(final COWArrayList<TickThreadRunner> runners) {
@@ -350,14 +350,14 @@ public void schedule(final SchedulableTick tick) {
 
     @Override
     public void notifyTasks(final SchedulableTick tick) {
-        if (tick.state instanceof ScheduledState state) {
+        if (tick.getState() instanceof ScheduledState state) {
             state.scheduleTasks();
         }
     }
 
     @Override
     public boolean cancel(final SchedulableTick tick) {
-        if (tick.state instanceof ScheduledState state) {
+        if (tick.getState() instanceof ScheduledState state) {
             return state.tryCancel();
         } else {
             return false;