diff --git a/java/missionary/Cancelled.java b/java/missionary/Cancelled.java
new file mode 100644
index 0000000..a9f14cd
--- /dev/null
+++ b/java/missionary/Cancelled.java
@@ -0,0 +1,11 @@
+package missionary;
+
+public class Cancelled extends Throwable {
+    public Cancelled() {
+        this(null);
+    }
+
+    public Cancelled(String message) {
+        super(message, null, false, false);
+    }
+}
diff --git a/java/missionary/impl/Ambiguous.java b/java/missionary/impl/Ambiguous.java
index 0b5f1ed..ffef542 100644
--- a/java/missionary/impl/Ambiguous.java
+++ b/java/missionary/impl/Ambiguous.java
@@ -1,6 +1,7 @@
 package missionary.impl;
 
 import clojure.lang.*;
+import missionary.Cancelled;
 
 import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
@@ -259,11 +260,9 @@ final class Gather implements Fiber {
 
         @Override
         public Object poll() {
-            if (choice == null ? token == null :
-                    choice.token == null || (choice.type == Choice.SWITCH && choice.ready == null && !choice.done))
-                throw new ExceptionInfo("Process cancelled.", RT.map(
-                        Keyword.intern(null, "cancelled"), Keyword.intern("missionary", "ap")));
-            return null;
+            return choice == null ? token == null :
+                    choice.token == null || (choice.type == Choice.SWITCH && choice.ready == null && !choice.done) ?
+                clojure.lang.Util.sneakyThrow(new Cancelled("Process cancelled.")) : null;
         }
 
         @Override
diff --git a/java/missionary/impl/Dataflow.java b/java/missionary/impl/Dataflow.java
index 49a797e..36cb781 100644
--- a/java/missionary/impl/Dataflow.java
+++ b/java/missionary/impl/Dataflow.java
@@ -1,6 +1,7 @@
 package missionary.impl;
 
 import clojure.lang.*;
+import missionary.Cancelled;
 
 import java.util.Iterator;
 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
@@ -53,9 +54,7 @@ public void cancel(Event e) {
             IPersistentSet set = (IPersistentSet) s;
             if (!(set.contains(e))) break;
             if (STATE.compareAndSet(this, s, set.count() == 1 ? null : set.disjoin(e))) {
-                e.failure.invoke(new ExceptionInfo("Dataflow variable derefence cancelled.", RT.map(
-                        Keyword.intern(null, "cancelled"),
-                        Keyword.intern("missionary", "dfv-deref"))));
+                e.failure.invoke(new Cancelled("Dataflow variable derefence cancelled."));
                 break;
             }
         }
diff --git a/java/missionary/impl/Enumerate.java b/java/missionary/impl/Enumerate.java
index 2fee44e..1bcb447 100644
--- a/java/missionary/impl/Enumerate.java
+++ b/java/missionary/impl/Enumerate.java
@@ -1,6 +1,7 @@
 package missionary.impl;
 
 import clojure.lang.*;
+import missionary.Cancelled;
 
 import java.util.Iterator;
 
@@ -38,9 +39,7 @@ public Object deref() {
         Iterator i = iterator;
         if (i == null) {
             terminator.invoke();
-            throw new ExceptionInfo("Enumeration cancelled.", RT.map(
-                    Keyword.intern(null, "cancelled"),
-                    Keyword.intern("missionary", "enumerate")));
+            clojure.lang.Util.sneakyThrow(new Cancelled("Seed cancelled."));
         }
         Object x = i.next();
         more(i);
diff --git a/java/missionary/impl/Fiber.java b/java/missionary/impl/Fiber.java
index 00df5a7..cb2568a 100644
--- a/java/missionary/impl/Fiber.java
+++ b/java/missionary/impl/Fiber.java
@@ -1,6 +1,7 @@
 package missionary.impl;
 
 import clojure.lang.*;
+import missionary.Cancelled;
 
 import java.util.concurrent.CountDownLatch;
 import java.util.function.Supplier;
@@ -10,9 +11,8 @@ public interface Fiber {
         Fiber THREAD = new Fiber() {
             @Override
             public Object poll() {
-                if (Thread.currentThread().isInterrupted())
-                    throw new ExceptionInfo("Thread interrupted.", PersistentArrayMap.EMPTY);
-                return null;
+                return Thread.currentThread().isInterrupted() ?
+                        clojure.lang.Util.sneakyThrow(new Cancelled("Thread interrupted.")) : null;
             }
 
             @Override
diff --git a/java/missionary/impl/GroupBy.java b/java/missionary/impl/GroupBy.java
index 87270a1..335f827 100644
--- a/java/missionary/impl/GroupBy.java
+++ b/java/missionary/impl/GroupBy.java
@@ -1,13 +1,10 @@
 package missionary.impl;
 
 import clojure.lang.*;
+import missionary.Cancelled;
 
 public interface GroupBy {
 
-    Throwable CANCELLED = new ExceptionInfo("Group consumer cancelled.", RT.map(
-            Keyword.intern(null, "cancelled"),
-            Keyword.intern("missionary", "group-by")));
-
     class Process extends AFn implements IDeref {
 
         static {
@@ -136,7 +133,7 @@ static Object consume(Group g) {
         Process p = g.process;
         if (p == null) {
             g.terminator.invoke();
-            return clojure.lang.Util.sneakyThrow(CANCELLED);
+            return clojure.lang.Util.sneakyThrow(new Cancelled("Group consumer cancelled."));
         } else synchronized (p) {
             Object v = p.value;
             p.value = p;
diff --git a/java/missionary/impl/Mailbox.java b/java/missionary/impl/Mailbox.java
index 1484d05..11bf8a0 100644
--- a/java/missionary/impl/Mailbox.java
+++ b/java/missionary/impl/Mailbox.java
@@ -1,6 +1,7 @@
 package missionary.impl;
 
 import clojure.lang.*;
+import missionary.Cancelled;
 
 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
 
@@ -61,9 +62,7 @@ public void cancel(Event e) {
             IPersistentSet set = (IPersistentSet) s;
             if (!(set.contains(e))) break;
             if (STATE.compareAndSet(this, s, set.count() == 1 ? null : set.disjoin(e))) {
-                e.failure.invoke(new ExceptionInfo("Mailbox fetch cancelled.", RT.map(
-                        Keyword.intern(null, "cancelled"),
-                        Keyword.intern("missionary", "mbx-fetch"))));
+                e.failure.invoke(new Cancelled("Mailbox fetch cancelled."));
                 break;
             }
         }
diff --git a/java/missionary/impl/Never.java b/java/missionary/impl/Never.java
index aedfcfe..ba88076 100644
--- a/java/missionary/impl/Never.java
+++ b/java/missionary/impl/Never.java
@@ -1,6 +1,7 @@
 package missionary.impl;
 
 import clojure.lang.*;
+import missionary.Cancelled;
 
 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
 
@@ -18,9 +19,7 @@ public Never(IFn f) {
     public Object invoke() {
         IFn f = failure;
         if (f != null && FAILURE.compareAndSet(this, f, null))
-            f.invoke(new ExceptionInfo("Never cancelled.", RT.map(
-                    Keyword.intern(null, "cancelled"),
-                    Keyword.intern("missionary", "never"))));
+            f.invoke(new Cancelled("Never cancelled."));
         return null;
     }
 }
diff --git a/java/missionary/impl/Rendezvous.java b/java/missionary/impl/Rendezvous.java
index 4a85e49..9ac5b1d 100644
--- a/java/missionary/impl/Rendezvous.java
+++ b/java/missionary/impl/Rendezvous.java
@@ -1,6 +1,7 @@
 package missionary.impl;
 
 import clojure.lang.*;
+import missionary.Cancelled;
 
 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
 
@@ -47,9 +48,7 @@ public void cancel(Event e) {
                 IPersistentSet set = (IPersistentSet) s;
                 if (!(set.contains(e))) break;
                 if (STATE.compareAndSet(Rendezvous.this, s, set.count() == 1 ? null : set.disjoin(e))) {
-                    e.failure.invoke(new ExceptionInfo("Rendez-vous give cancelled.", RT.map(
-                            Keyword.intern(null, "cancelled"),
-                            Keyword.intern("missionary", "rdv-give"))));
+                    e.failure.invoke(new Cancelled("Rendez-vous give cancelled."));
                     break;
                 }
             }
@@ -89,9 +88,7 @@ public void cancel(Event e) {
             IPersistentSet set = (IPersistentSet) s;
             if (!(set.contains(e))) break;
             if (STATE.compareAndSet(this, s, set.count() == 1 ? null : set.disjoin(e))) {
-                e.failure.invoke(new ExceptionInfo("Rendez-vous take cancelled.", RT.map(
-                        Keyword.intern(null, "cancelled"),
-                        Keyword.intern("missionary", "rdv-take"))));
+                e.failure.invoke(new Cancelled("Rendez-vous take cancelled."));
                 break;
             }
         }
diff --git a/java/missionary/impl/Semaphore.java b/java/missionary/impl/Semaphore.java
index 5b9dd93..8e787b1 100644
--- a/java/missionary/impl/Semaphore.java
+++ b/java/missionary/impl/Semaphore.java
@@ -1,6 +1,7 @@
 package missionary.impl;
 
 import clojure.lang.*;
+import missionary.Cancelled;
 
 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
 
@@ -59,9 +60,7 @@ public void cancel(Event e) {
             IPersistentSet set = (IPersistentSet) s;
             if (!(set.contains(e))) break;
             if (STATE.compareAndSet(this, s, set.count() == 1 ? null : set.disjoin(e))) {
-                e.failure.invoke(new ExceptionInfo("Semaphore acquire cancelled.", RT.map(
-                        Keyword.intern(null, "cancelled"),
-                        Keyword.intern("missionary", "sem-acquire"))));
+                e.failure.invoke(new Cancelled("Semaphore acquire cancelled."));
                 break;
             }
         }
diff --git a/java/missionary/impl/Sequential.java b/java/missionary/impl/Sequential.java
index db59fb0..cf3be97 100644
--- a/java/missionary/impl/Sequential.java
+++ b/java/missionary/impl/Sequential.java
@@ -1,6 +1,7 @@
 package missionary.impl;
 
 import clojure.lang.*;
+import missionary.Cancelled;
 
 import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
@@ -76,9 +77,7 @@ public Object invoke() {
 
     @Override
     public Object poll() {
-        if (token == null) throw new ExceptionInfo("Process cancelled.", RT.map(
-                Keyword.intern(null, "cancelled"), Keyword.intern("missionary", "sp")));
-        return null;
+        return token == null ? clojure.lang.Util.sneakyThrow(new Cancelled("Process cancelled.")) : null;
     }
 
     @Override
diff --git a/java/missionary/impl/Sleep.java b/java/missionary/impl/Sleep.java
index b59e63b..13e66c8 100644
--- a/java/missionary/impl/Sleep.java
+++ b/java/missionary/impl/Sleep.java
@@ -1,6 +1,7 @@
 package missionary.impl;
 
 import clojure.lang.*;
+import missionary.Cancelled;
 
 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
 
@@ -49,9 +50,7 @@ void cancel(Sleep s) {
                     if (ss.equals(item)) break; else n = p.assoc(s.time, ss);
                 }
                 if (PENDING.compareAndSet(this, p, n)) {
-                    s.failure.invoke(new ExceptionInfo("Sleep cancelled.", RT.map(
-                            Keyword.intern(null, "cancelled"),
-                            Keyword.intern("missionary", "sleep"))));
+                    s.failure.invoke(new Cancelled("Sleep cancelled."));
                     break;
                 }
             }
diff --git a/java/missionary/impl/Sub.java b/java/missionary/impl/Sub.java
index 75c137b..bc38de2 100644
--- a/java/missionary/impl/Sub.java
+++ b/java/missionary/impl/Sub.java
@@ -1,6 +1,7 @@
 package missionary.impl;
 
 import clojure.lang.*;
+import missionary.Cancelled;
 import org.reactivestreams.Publisher;
 import org.reactivestreams.Subscriber;
 import org.reactivestreams.Subscription;
@@ -79,10 +80,7 @@ public Object deref() {
                     Object x = current;
                     if (x == null) {
                         terminator.invoke();
-                        throw new ExceptionInfo("Subscription cancelled.", RT.map(
-                                Keyword.intern(null, "cancelled"),
-                                Keyword.intern("missionary", "subscribe")
-                        ));
+                        clojure.lang.Util.sneakyThrow(new Cancelled("Subscription cancelled."));
                     } else {
                         current = null;
                         notifier.invoke();
diff --git a/src/missionary/Cancelled.js b/src/missionary/Cancelled.js
new file mode 100644
index 0000000..9dc53b9
--- /dev/null
+++ b/src/missionary/Cancelled.js
@@ -0,0 +1,16 @@
+goog.provide('missionary.Cancelled');
+
+/**
+ * @param {string} message
+ * @constructor
+ */
+missionary.Cancelled = function(message) {
+  'use strict';
+
+  /**
+   * The error message.
+   * @const {string}
+   */
+  this.message = message;
+
+};
diff --git a/src/missionary/impl.cljs b/src/missionary/impl.cljs
index ffc7c22..189e1e1 100644
--- a/src/missionary/impl.cljs
+++ b/src/missionary/impl.cljs
@@ -1,4 +1,5 @@
-(ns ^:no-doc missionary.impl)
+(ns ^:no-doc missionary.impl
+  (:import missionary.Cancelled))
 
 (defn nop [])
 
@@ -41,8 +42,7 @@
         #(when-not bound
            (when (contains? watch !)
              (set! watch (disj! watch !))
-             (f! (ex-info "Dataflow variable dereference cancelled."
-                          {:cancelled :missionary/dfv-deref}))))))))
+             (f! (Cancelled. "Dataflow variable dereference cancelled."))))))))
 
 (defn dataflow []
   (->Dataflow false nil (transient #{})))
@@ -64,8 +64,7 @@
           (set! writers (assoc writers ! t))
           #(when (contains? writers !)
              (set! writers (dissoc writers !))
-             (f! (ex-info "Rendez-vous give cancelled."
-                          {:cancelled :missionary/rdv-give})))))))
+             (f! (Cancelled. "Rendez-vous give cancelled.")))))))
   (-invoke [_ s! f!]
     (if-some [[[! t]] (seq writers)]
       (do (set! writers (dissoc writers !))
@@ -74,8 +73,7 @@
         (set! readers (conj readers !))
         #(when (contains? readers !)
            (set! readers (disj readers !))
-           (f! (ex-info "Rendez-vous take cancelled."
-                        {:cancelled :missionary/rdv-take})))))))
+           (f! (Cancelled. "Rendez-vous take cancelled.")))))))
 
 (defn rendezvous []
   (->Rendezvous #{} {}))
@@ -100,7 +98,7 @@
           (set! readers (conj readers !))
           #(when (contains? readers !)
              (set! readers (disj readers !))
-             (f! (ex-info "Mailbox fetch cancelled." {:cancelled :missionary/mbx-fetch}))))
+             (f! (Cancelled. "Mailbox fetch cancelled."))))
         (let [tmp enqueue]
           (set! enqueue dequeue)
           (set! dequeue (.reverse tmp))
@@ -128,7 +126,7 @@
         (set! readers (conj readers !))
         #(when (contains? readers !)
            (set! readers (disj readers !))
-           (f! (ex-info "Semaphore acquire cancelled." {:cancelled :missionary/sem-acquire}))))
+           (f! (Cancelled. "Semaphore acquire cancelled."))))
       (do (set! available (dec available))
           (s! nil) nop))))
 
@@ -200,7 +198,7 @@
   (when (.-pending s)
     (set! (.-pending s) false)
     (js/clearTimeout (.-handler s))
-    ((.-failure s) (ex-info "Sleep cancelled." {:cancelled :missionary/sleep}))))
+    ((.-failure s) (Cancelled. "Sleep cancelled."))))
 
 (defn sleep [d x s f]
   (let [slp (->Sleep f nil true)]
@@ -225,7 +223,7 @@
   (-invoke [_]
     (when alive
       (set! alive false)
-      (f (ex-info "Never cancelled." {:cancelled :missionary/never})))))
+      (f (Cancelled. "Never cancelled.")))))
 
 (defn never [f] (->Never f true))
 
@@ -260,7 +258,7 @@
   Fiber
   (poll [_]
     (when (nil? token)
-      (throw (ex-info "Process cancelled." {:cancelled :missionary/sp}))))
+      (throw (Cancelled. "Process cancelled."))))
   (task [_ t]
     (let [c (t resume rethrow)]
       (if (nil? token)
@@ -329,7 +327,7 @@
                      (nil? (.-ready c))
                      (not (.-done c))))
             (nil? token))
-      (throw (ex-info "Process cancelled." {:cancelled :missionary/ap}))))
+      (throw (Cancelled. "Process cancelled."))))
   (task [_ t]
     (ap-swap _ (t resume rethrow)) nop)
   (flow-concat [_ f]
@@ -527,8 +525,7 @@
     (let [x (.next i)]
       (enumerate-pull e) x)
     (do ((.-terminator e))
-        (throw (ex-info "Enumeration cancelled"
-                        {:cancelled :missionary/enumerate})))))
+        (throw (Cancelled. "Seed cancelled")))))
 
 (defn enumerate [coll n t]
   (doto (->Enumerate (iter coll) n t) (enumerate-pull)))
diff --git a/src/missionary/impl/GroupBy.cljs b/src/missionary/impl/GroupBy.cljs
index 810c182..c26e920 100644
--- a/src/missionary/impl/GroupBy.cljs
+++ b/src/missionary/impl/GroupBy.cljs
@@ -1,6 +1,5 @@
-(ns ^:no-doc missionary.impl.GroupBy)
-
-(def cancelled (ex-info "Group consumer cancelled." {:cancelled :missionary/group-by}))
+(ns ^:no-doc missionary.impl.GroupBy
+  (:import missionary.Cancelled))
 
 (declare sample cancel consume)
 
@@ -120,7 +119,7 @@
       (set! (.-key p) p)
       (transfer p) x)
     (do ((.-terminator g))
-        (throw cancelled))))
+        (throw (Cancelled. "Group consumer cancelled.")))))
 
 (defn run [k f n t]
   (let [p (->Process k n t nil nil nil (object-array 8) 0 true false)]
diff --git a/test/missionary/core_test.cljc b/test/missionary/core_test.cljc
index 560a313..d21e843 100644
--- a/test/missionary/core_test.cljc
+++ b/test/missionary/core_test.cljc
@@ -1,7 +1,8 @@
 (ns missionary.core-test
   (:require
     [missionary.core :as m :include-macros true]
-    [missionary.tck :refer [if-try deftask defflow] :include-macros true]))
+    [missionary.tck :refer [if-try deftask defflow] :include-macros true])
+  (:import missionary.Cancelled))
 
 (def =? (partial partial =))
 (def fine! #(throw (ex-info "this is fine." {:fine true})))
@@ -18,7 +19,7 @@ https://stackoverflow.com/questions/12925988/how-to-generate-strings-that-share-
 (deftask sleep-failure
   {:cancel  0
    :timeout 10
-   :failure (comp :cancelled ex-data)}
+   :failure (partial instance? Cancelled)}
   (m/sleep 100))
 
 (deftask semaphore
@@ -36,7 +37,7 @@ https://stackoverflow.com/questions/12925988/how-to-generate-strings-that-share-
 (deftask rendezvous
   {:cancel 150
    :timeout 200
-   :failure (comp :cancelled ex-data)}
+   :failure (partial instance? Cancelled)}
   (m/sp
     (let [rdv (m/rdv)]
       (m/? (->> (m/sp (while true
@@ -51,7 +52,7 @@ https://stackoverflow.com/questions/12925988/how-to-generate-strings-that-share-
 (deftask mailbox
   {:cancel 150
    :timeout 200
-   :failure (comp :cancelled ex-data)}
+   :failure (partial instance? Cancelled)}
   (m/sp
     (let [mbx (m/mbx)]
       (m/? (->> (m/sp (while true