diff --git a/host/chez/java/natives-array.ss b/host/chez/java/natives-array.ss
index 403639a..68c14b8 100644
--- a/host/chez/java/natives-array.ss
+++ b/host/chez/java/natives-array.ss
@@ -109,9 +109,24 @@
        (let* ((v (cseq-cvec s)) (i (cseq-ci s)))
          (cons v (fxmin (fx+ i na-chunk-size) (pvec-count v))))))
 (define (na-chunked-seq? x) (and (na-vblock x) #t))
+;; Copy the block [i, end) straight out of the pvec trie's 32-element leaf node
+;; (pv-chunk-for is O(log n)). na-chunk-size == pv-width and blocks are 32-aligned,
+;; so a block is exactly one leaf; the rare non-aligned window crossing a leaf
+;; boundary falls back to per-index reads. Flattening the whole backing vector
+;; per block (pvec-v) made chunk-first O(n), so walking a vector chunk-by-chunk
+;; was O(n^2).
 (define (na-chunk-first s)
   (let ((vb (na-vblock s)))
-    (if vb (make-pvec (vec-copy-range (pvec-v (car vb)) (cseq-ci s) (cdr vb)))
+    (if vb
+        (let* ((pv (car vb)) (i (cseq-ci s)) (end (cdr vb)) (len (fx- end i))
+               (node (pv-chunk-for pv i)) (off (fxand i pv-mask)))
+          (if (fx<=? (fx+ off len) (vector-length node))
+              (make-pvec (vec-copy-range node off (fx+ off len)))
+              (let ((out (make-vector len)))
+                (let loop ((j 0))
+                  (if (fx<? j len)
+                      (begin (vector-set! out j (pvec-nth-d pv (fx+ i j) jolt-nil)) (loop (fx+ j 1)))
+                      (make-pvec out))))))
         (jolt-first s))))               ; eager-buffer fallback
 (define (na-chunk-rest s)
   (let ((vb (na-vblock s)))
diff --git a/test/chez/corpus.edn b/test/chez/corpus.edn
index 7fe562e..aca2fc1 100644
--- a/test/chez/corpus.edn
+++ b/test/chez/corpus.edn
@@ -1640,7 +1640,7 @@
   {:suite "predicates / tagged-value" :label "tagged-literal? yes" :expected "true" :actual "(tagged-literal? (tagged-literal (quote inst) \"2020\"))"}
   {:suite "predicates / tagged-value" :label "tagged-literal? no" :expected "false" :actual "(tagged-literal? 1)"}
   {:suite "predicates / tagged-value" :label "reader-conditional? no" :expected "false" :actual "(reader-conditional? 1)"}
-  {:suite "predicates / tagged-value" :label "chunked-seq? always false" :expected "true" :actual "(chunked-seq? (seq [1 2 3]))"}
+  {:suite "predicates / tagged-value" :label "chunked-seq? true for a vector seq" :expected "true" :actual "(chunked-seq? (seq [1 2 3]))"}
   {:suite "predicates / equality & identity" :label "= same" :expected "true" :actual "(= 1 1)"}
   {:suite "predicates / equality & identity" :label "= vectors" :expected "true" :actual "(= [1 2] [1 2])"}
   {:suite "predicates / equality & identity" :label "= vector & list" :expected "true" :actual "(= [1 2] (list 1 2))"}
@@ -2709,6 +2709,11 @@
   {:suite "untested / chunk family (eager equivalents) + cat" :label "halt-when" :expected "4" :actual "(transduce (halt-when even?) conj [] [1 3 4 5])"}
   {:suite "untested / chunk family (eager equivalents) + cat" :label "chunk-next exhausted" :expected "nil" :actual "(let [cb (chunk-buffer 2)] (chunk-append cb 1) (chunk-next (chunk-cons (chunk cb) nil)))"}
   {:suite "untested / chunk family (eager equivalents) + cat" :label "chunk-rest seqable" :expected "[]" :actual "(let [cb (chunk-buffer 2)] (chunk-append cb 1) (vec (chunk-rest (chunk-cons (chunk cb) nil))))"}
+  {:suite "chunked-seq / over a vector" :label "chunk-first is a 32-element block" :expected "32" :actual "(count (chunk-first (seq (vec (range 100)))))"}
+  {:suite "chunked-seq / over a vector" :label "chunked-seq? true for vector seq" :expected "true" :actual "(chunked-seq? (seq (vec (range 100))))"}
+  {:suite "chunked-seq / over a vector" :label "chunked-seq? false for a list seq" :expected "false" :actual "(chunked-seq? (seq (list 1 2 3)))"}
+  {:suite "chunked-seq / over a vector" :label "chunk-first contents + chunk-rest boundary" :expected "[32 0 31 32]" :actual "(let [s (seq (vec (range 50))) c (chunk-first s)] [(count c) (nth c 0) (nth c 31) (first (chunk-rest s))])"}
+  {:suite "chunked-seq / over a vector" :label "chunk-first window past the first block" :expected "[32 33 34 35 36 37 38 39]" :actual "(vec (chunk-first (chunk-rest (seq (vec (range 40))))))"}
   {:suite "untested / JVM-shape stubs (documented jolt behavior)" :label "class number" :expected "java.lang.Long" :actual "(class 1)"}
   {:suite "untested / JVM-shape stubs (documented jolt behavior)" :label "class string" :expected "java.lang.String" :actual "(class \"s\")"}
   {:suite "untested / JVM-shape stubs (documented jolt behavior)" :label "class keyword" :expected "clojure.lang.Keyword" :actual "(class :k)"}