diff --git a/host/chez/records.ss b/host/chez/records.ss
index eb21e91..3a3d880 100644
--- a/host/chez/records.ss
+++ b/host/chez/records.ss
@@ -255,10 +255,21 @@
 ;; &message text plus any &irritants, or display-condition output as a fallback.
 (define (condition->message-string c)
   (if (message-condition? c)
-      (let ((m (condition-message c))
-            (irr (if (irritants-condition? c) (condition-irritants c) '())))
-        (let loop ((xs irr) (acc m))
-          (if (null? xs) acc (loop (cdr xs) (string-append acc " " (jolt-pr-str (car xs)))))))
+      (let* ((m (condition-message c))
+             (irr (if (irritants-condition? c) (condition-irritants c) '()))
+             (append-irr (lambda ()
+                           (let loop ((xs irr) (acc m))
+                             (if (null? xs) acc
+                                 (loop (cdr xs) (string-append acc " " (jolt-pr-str (car xs)))))))))
+        ;; some Chez conditions (open-input-file etc.) carry a format-template
+        ;; message ("failed for ~a: ~(~a~)") whose irritants fill the directives;
+        ;; format it in. Fall back to appending the irritants if that fails.
+        (if (and (string? m) (let scan ((i 0))
+                               (cond ((>= i (string-length m)) #f)
+                                     ((char=? (string-ref m i) #\~) #t)
+                                     (else (scan (+ i 1))))))
+            (guard (e (#t (append-irr))) (apply format m irr))
+            (append-irr)))
       (with-output-to-string (lambda () (display-condition c)))))
 ;; expose a Chez condition's message to Clojure (ex-message returns nil for raw
 ;; host conditions): the nREPL eval handler surfaces it instead of an opaque
diff --git a/stdlib/clojure/test.clj b/stdlib/clojure/test.clj
index 46d722e..789c350 100644
--- a/stdlib/clojure/test.clj
+++ b/stdlib/clojure/test.clj
@@ -46,6 +46,14 @@
 (defn n-error [] (:error @counters))
 (defn failures [] (:fails @counters))
 
+;; Message of a thrown value: ex-info's message, else a raw host condition's text
+;; (ex-message is nil for those), else its printed form — so a crash is never
+;; reported with a blank message.
+(defn err-text [e]
+  (or (ex-message e)
+      (jolt.host/condition-message e)
+      (str e)))
+
 ;; clojure.test/report multimethod — present so suites that add reporting
 ;; methods (defmethod clojure.test/report :begin-test-var ...) load. The runner
 ;; below does its own console output and doesn't dispatch through it.
@@ -110,7 +118,7 @@
           (clojure.test/inc-pass!)
           (clojure.test/fail! (str (pr-str '~form) (when ~msg (str " — " ~msg)))))
         (catch Throwable e#
-          (clojure.test/err! (str (pr-str '~form) " threw: " (clojure.core/ex-message e#))))))))
+          (clojure.test/err! (str (pr-str '~form) " threw: " (clojure.test/err-text e#))))))))
 
 (defmacro testing [s & body]
   `(do
@@ -152,7 +160,7 @@
       (try
         ((:fn t))
         (catch Throwable e
-          (err! (str (:name t) " crashed: " (clojure.core/ex-message e))))))))
+          (err! (str (:name t) " crashed: " (err-text e))))))))
 
 (defn run-registered []
   (doseq [t @registry] (run-one t))