diff --git a/os2.rkt b/os2.rkt
index 6e6a833..e788d9d 100644
--- a/os2.rkt
+++ b/os2.rkt
@@ -193,30 +193,33 @@
 					      hs))]))
 
 (define (do-unsubscribe pid eid reason state)
-  (define endpoint-to-remove (hash-ref (vm-endpoints state) eid))
-  (define removed-topic (endpoint-topic endpoint-to-remove))
-  (define old-process (hash-ref (vm-processes state) pid))
-  (define new-process (struct-copy process old-process
-				   [endpoints (set-remove (process-endpoints old-process) eid)]))
-  (let ((state (struct-copy vm state
-			    [endpoints (hash-remove (vm-endpoints state) eid)]
-			    [processes (if (set-empty? (process-endpoints new-process))
-					   (hash-remove (vm-processes state) pid)
-					   (hash-set (vm-processes state) pid new-process))])))
-    (for*/fold ([state state])
-	([(matching-pid p) (in-hash (vm-processes state))]
-	 [matching-eid (in-set (process-endpoints p))]
-	 [e (in-value (hash-ref (vm-endpoints state) matching-eid))]
-	 [matching-topic (in-value (endpoint-topic e))]
-	 [flow-pattern (in-value (topic-intersection removed-topic matching-topic))]
-	 #:when flow-pattern)
-      (define outbound-flow (refine-topic removed-topic flow-pattern))
-      (run-trapk state
-		 matching-pid
-		 (handlers-absence (endpoint-handlers e))
-		 matching-eid
-		 outbound-flow
-		 reason))))
+  (cond
+   [(hash-has-key? (vm-endpoints state) eid)
+    (define endpoint-to-remove (hash-ref (vm-endpoints state) eid))
+    (define removed-topic (endpoint-topic endpoint-to-remove))
+    (define old-process (hash-ref (vm-processes state) pid))
+    (define new-process (struct-copy process old-process
+				     [endpoints (set-remove (process-endpoints old-process) eid)]))
+    (let ((state (struct-copy vm state
+			      [endpoints (hash-remove (vm-endpoints state) eid)]
+			      [processes (if (set-empty? (process-endpoints new-process))
+					     (hash-remove (vm-processes state) pid)
+					     (hash-set (vm-processes state) pid new-process))])))
+      (for*/fold ([state state])
+	  ([(matching-pid p) (in-hash (vm-processes state))]
+	   [matching-eid (in-set (process-endpoints p))]
+	   [e (in-value (hash-ref (vm-endpoints state) matching-eid))]
+	   [matching-topic (in-value (endpoint-topic e))]
+	   [flow-pattern (in-value (topic-intersection removed-topic matching-topic))]
+	   #:when flow-pattern)
+	(define outbound-flow (refine-topic removed-topic flow-pattern))
+	(run-trapk state
+		   matching-pid
+		   (handlers-absence (endpoint-handlers e))
+		   matching-eid
+		   outbound-flow
+		   reason)))]
+   [else state]))
 
 (define (route-and-deliver message-topic body state)
   (define pids-and-endpoints