diff --git a/host/chez/run-corpus.ss b/host/chez/run-corpus.ss
index 0c97938..417c922 100644
--- a/host/chez/run-corpus.ss
+++ b/host/chez/run-corpus.ss
@@ -11,7 +11,7 @@
 ;; reset between cases so there is no leakage — same isolation a fresh process gives.
 ;;
 ;;   chez --script host/chez/run-corpus.ss
-;;   JOLT_CHEZ_ZJ_FLOOR=N   override the regression floor (default 2688)
+;;   JOLT_CHEZ_ZJ_FLOOR=N   override the regression floor (default 2690)
 ;;   JOLT_CORPUS_LIMIT=N    every-Nth stride (fast iteration; floor drops to 0)
 ;;   JOLT_DUMP_CRASH_LABELS=1   list crash + allowlisted labels
 (import (chezscheme))
@@ -203,7 +203,7 @@
 
 ;; Regression floor: fail on any NEW divergence or if pass drops below the floor.
 (define base-floor (let ((s (getenv "JOLT_CHEZ_ZJ_FLOOR")))
-                     (if s (string->number s) 2688)))
+                     (if s (string->number s) 2690)))
 (define floor (if limit 0 base-floor))
 (when (or (> (length diverged) 0) (< pass floor))
   (printf "REGRESSION: pass ~a < floor ~a or ~a new divergence(s)\n"
diff --git a/host/chez/transients.ss b/host/chez/transients.ss
index 0d6faea..923bddf 100644
--- a/host/chez/transients.ss
+++ b/host/chez/transients.ss
@@ -38,7 +38,13 @@
 ;; (assoc! t k v & kvs): variadic like Clojure (jolt-assoc already folds pairs).
 (define (jolt-assoc! t . kvs)
   (jolt-trans-check t "assoc!")
-  (jolt-transient-coll-set! t (apply jolt-assoc (jolt-transient-coll t) kvs))
+  ;; JVM assoc! is variadic: once a complete first key/val pair is present (>=3
+  ;; kvs), a TRAILING lone key fills nil; a lone key alone (1 kv) is a wrong-arity
+  ;; throw (so don't pad it — the persistent assoc raises on odd args).
+  (let ((kvs (if (and (>= (length kvs) 3) (odd? (length kvs)))
+                 (append kvs (list jolt-nil))
+                 kvs)))
+    (jolt-transient-coll-set! t (apply jolt-assoc (jolt-transient-coll t) kvs)))
   t)
 (define (jolt-dissoc! t . ks)
   (jolt-trans-check t "dissoc!")