diff --git a/CHANGELOG.md b/CHANGELOG.md
index 09a2674f..f9585bf4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- `dev.vortex:vortex-jni` 0.84.0 → 0.85.0; vortex-jni's writer no longer emits a per-zone `SUM` in the `vortex.zoned` stats table (upstream: a zone sum prunes nothing and its null-on-empty semantics were unsettled), so `ZoneReducer#sum` now falls back to a full scan for Rust-written files instead of pushing the reduction down. ([#360](https://github.com/dfa1/vortex-java/pull/360))
+
 ## [0.13.3] — 2026-08-15
 
 Nested Parquet import, plus a cluster of real correctness bugs (three writer-side, one reader-side)
diff --git a/integration/src/test/java/io/github/dfa1/vortex/integration/RustWritesJavaReadsIntegrationTest.java b/integration/src/test/java/io/github/dfa1/vortex/integration/RustWritesJavaReadsIntegrationTest.java
index c1b15669..b8384d42 100644
--- a/integration/src/test/java/io/github/dfa1/vortex/integration/RustWritesJavaReadsIntegrationTest.java
+++ b/integration/src/test/java/io/github/dfa1/vortex/integration/RustWritesJavaReadsIntegrationTest.java
@@ -248,10 +248,16 @@ void jniWriter_javaReader_singleChunk(@TempDir Path tmp) throws IOException {
     }
 
     @Test
-    void jniWriter_perZoneSum_readFromZoneMapTable(@TempDir Path tmp) throws IOException {
+    void jniWriter_noPerZoneSum_zoneReducerSignalsFallbackAndDecodeStillCorrect(@TempDir Path tmp)
+            throws IOException {
         // Given — a Rust-written file large enough that the JNI writer emits a multi-zone column.
-        // Sum lives only in Rust's vortex.stats zone-map table (its flat writer doesn't retain it),
-        // so this proves the Java reader decodes that table for per-zone SUM (ADR 0013 §6 parity).
+        // vortex-jni 0.85.0 dropped SUM from the zone-map aggregate defaults (a zone sum prunes
+        // nothing, and its null-on-empty semantics were unsettled — see spiraldb/vortex#9206's
+        // writer comment), so zones now carry only MAX/MIN/NAN_COUNT/NULL_COUNT. This proves the
+        // Java reader reflects that absence faithfully (no fabricated SUM), that
+        // [io.github.dfa1.vortex.reader.compute.ZoneReducer#sum(String)] signals the caller to fall
+        // back instead of under-counting, and that decoding the column directly still yields the
+        // right total.
         int n = 200_000;
         long[] ids = new long[n];
         double[] vals = new double[n];
@@ -263,15 +269,22 @@ void jniWriter_perZoneSum_readFromZoneMapTable(@TempDir Path tmp) throws IOExcep
         writeJni(file, ids, vals);
         long expected = (long) n * (n - 1) / 2; // Σ 0..n-1
 
-        // When — fold the per-zone SUM rows the reader surfaces from the zone-map table
+        // When / Then — no zone carries a SUM statistic anymore
         try (var vf = VortexReader.open(file, ReadRegistry.loadAll());
              var iter = vf.scan(io.github.dfa1.vortex.reader.ScanOptions.all())) {
             List<ArrayStats> zones = iter.columnZoneStats("id");
+            assertThat(zones).isNotEmpty().allSatisfy(z -> assertThat(z.sum()).isNull());
+        }
+
+        // When / Then — the reducer refuses to guess and tells the caller to stream instead
+        try (var vf = VortexReader.open(file, ReadRegistry.loadAll())) {
+            Number pushedDown = new io.github.dfa1.vortex.reader.compute.ZoneReducer(vf).sum("id");
+            assertThat(pushedDown).isNull();
+        }
 
-            // Then — every zone carries a SUM (came from Rust's table, not a Java-side recompute)
-            // and the whole-zone fold equals the column total.
-            assertThat(zones).isNotEmpty().allSatisfy(z -> assertThat(z.sum()).isNotNull());
-            long total = zones.stream().mapToLong(z -> (Long) z.sum()).sum();
+        // When / Then — decoding the column the ordinary way still returns the exact total
+        try (var vf = VortexReader.open(file, ReadRegistry.loadAll())) {
+            long total = scanAll(vf).stream().flatMapToLong(c -> Arrays.stream(ids(c))).sum();
             assertThat(total).isEqualTo(expected);
         }
     }
diff --git a/pom.xml b/pom.xml
index 2ce37abb..4bb678a5 100644
--- a/pom.xml
+++ b/pom.xml
@@ -73,7 +73,7 @@
 		<jazzer.version>0.30.0</jazzer.version>
 		<assertj.version>3.27.7</assertj.version>
 		<mockito.version>5.23.0</mockito.version>
-		<vortex-jni.version>0.84.0</vortex-jni.version>
+		<vortex-jni.version>0.85.0</vortex-jni.version>
 		<arrow.version>19.0.0</arrow.version>
 		<slf4j.version>2.0.18</slf4j.version>
 		<!-- coverage -->