diff --git a/src/ex/workqueue.zig b/src/ex/workqueue.zig
index dd9dd86..5ea3dc2 100644
--- a/src/ex/workqueue.zig
+++ b/src/ex/workqueue.zig
@@ -123,6 +123,10 @@ pub fn enqueue(item: *WorkItem) void {
     const ipl = ke.ipl.raise(.Dispatch);
     defer ke.ipl.lower(ipl);
 
+    if (item.enqueued.cmpxchgStrong(false, true, .acquire, .monotonic) != null) {
+        return;
+    }
+
     var pool: *Pool = undefined;
 
     switch (item.priority) {