diff --git a/imperative/assertions.rkt b/imperative/assertions.rkt
index c91e42d..6719a57 100644
--- a/imperative/assertions.rkt
+++ b/imperative/assertions.rkt
@@ -5,7 +5,12 @@
          (struct-out observe)
          (struct-out seal)
          (struct-out inbound)
-         (struct-out outbound))
+         (struct-out outbound)
+         strong-gensym)
+
+(require (only-in net/base64 base64-encode))
+(require (only-in racket/random crypto-random-bytes))
+(require (only-in racket/string string-trim))
 
 ;; Thin veneers over `struct` for declaring intent.
 (define-syntax-rule (assertion-struct item ...) (struct item ... #:prefab))
@@ -22,3 +27,11 @@
 
 (struct inbound (assertion) #:prefab)
 (struct outbound (assertion) #:prefab)
+
+(define (strong-gensym [head 'g] #:random-bytes [count 16])
+  (string->symbol
+   (format "~a~a"
+           head
+           (string-trim (bytes->string/latin-1
+                         (base64-encode (crypto-random-bytes count) #""))
+                        #px"=+"))))
diff --git a/imperative/examples/broker-chat-client.rkt b/imperative/examples/broker-chat-client.rkt
index 7e10808..b49deb3 100644
--- a/imperative/examples/broker-chat-client.rkt
+++ b/imperative/examples/broker-chat-client.rkt
@@ -8,7 +8,7 @@
 (message-struct Says (who what))
 
 (spawn #:name 'main
-       (field [username (symbol->string (gensym 'chatter))])
+       (field [username (symbol->string (strong-gensym 'chatter-))])
 
        (define root-facet (current-facet))
        (define url standard-localhost-broker/tcp)