diff --git a/packages/SwingSet/test/test-marshal.js b/packages/SwingSet/test/test-marshal.js
index 354019864e8..5fa3fc3f319 100644
--- a/packages/SwingSet/test/test-marshal.js
+++ b/packages/SwingSet/test/test-marshal.js
@@ -34,7 +34,7 @@ test('serialize static data', t => {
     body: '{"@qclass":"undefined"}',
     slots: [],
   });
-  t.deepEqual(ser(-0), { body: '{"@qclass":"-0"}', slots: [] });
+//  t.deepEqual(ser(-0), { body: '{"@qclass":"-0"}', slots: [] });
   t.deepEqual(ser(NaN), { body: '{"@qclass":"NaN"}', slots: [] });
   t.deepEqual(ser(Infinity), {
     body: '{"@qclass":"Infinity"}',
@@ -86,8 +86,8 @@ test('unserialize static data', t => {
 
   // JS primitives that aren't natively representable by JSON
   t.deepEqual(uns('{"@qclass":"undefined"}'), undefined);
-  t.ok(Object.is(uns('{"@qclass":"-0"}'), -0));
-  t.notOk(Object.is(uns('{"@qclass":"-0"}'), 0));
+//  t.ok(Object.is(uns('{"@qclass":"-0"}'), -0));
+//  t.notOk(Object.is(uns('{"@qclass":"-0"}'), 0));
   t.ok(Object.is(uns('{"@qclass":"NaN"}'), NaN));
   t.deepEqual(uns('{"@qclass":"Infinity"}'), Infinity);
   t.deepEqual(uns('{"@qclass":"-Infinity"}'), -Infinity);
diff --git a/packages/marshal/marshal.js b/packages/marshal/marshal.js
index 462f84a8cb5..59b21df5745 100644
--- a/packages/marshal/marshal.js
+++ b/packages/marshal/marshal.js
@@ -156,6 +156,17 @@ export function mustPassByPresence(val) {
   // ok!
 }
 
+// This is the equality comparison used by JavaScript's Map and Set
+// abstractions, where NaN is the same as NaN and -0 is the same as
+// 0. Marshal serializes -0 as zero, so the semantics of our distributed
+// object system does not distinguish 0 from -0.
+//
+// `sameValueZero` is the EcmaScript spec name for this equality comparison,
+// but TODO we need a better name for the API.
+export function sameValueZero(x, y) {
+  return x === y || Object.is(x, y);
+}
+
 // How would val be passed?  For primitive values, the answer is
 //   * 'null' for null
 //   * throwing an error for an unregistered symbol
@@ -343,7 +354,7 @@ export function makeMarshal(
             return harden({ [QCLASS]: 'NaN' });
           }
           if (Object.is(val, -0)) {
-            return harden({ [QCLASS]: '-0' });
+            return 0;
           }
           if (val === Infinity) {
             return harden({ [QCLASS]: 'Infinity' });
@@ -478,9 +489,6 @@ export function makeMarshal(
           case 'undefined': {
             return undefined;
           }
-          case '-0': {
-            return -0;
-          }
           case 'NaN': {
             return NaN;
           }
diff --git a/packages/marshal/test/test-marshal.js b/packages/marshal/test/test-marshal.js
index 23b73b46011..802874aae9f 100644
--- a/packages/marshal/test/test-marshal.js
+++ b/packages/marshal/test/test-marshal.js
@@ -19,7 +19,7 @@ test('serialize static data', t => {
     body: '{"@qclass":"undefined"}',
     slots: [],
   });
-  t.deepEqual(ser(-0), { body: '{"@qclass":"-0"}', slots: [] });
+//  t.deepEqual(ser(-0), { body: '{"@qclass":"-0"}', slots: [] });
   t.deepEqual(ser(NaN), { body: '{"@qclass":"NaN"}', slots: [] });
   t.deepEqual(ser(Infinity), {
     body: '{"@qclass":"Infinity"}',
@@ -75,8 +75,8 @@ test('unserialize static data', t => {
 
   // JS primitives that aren't natively representable by JSON
   t.deepEqual(uns('{"@qclass":"undefined"}'), undefined);
-  t.ok(Object.is(uns('{"@qclass":"-0"}'), -0));
-  t.notOk(Object.is(uns('{"@qclass":"-0"}'), 0));
+  //t.ok(Object.is(uns('{"@qclass":"-0"}'), -0));
+  //t.notOk(Object.is(uns('{"@qclass":"-0"}'), 0));
   t.ok(Object.is(uns('{"@qclass":"NaN"}'), NaN));
   t.deepEqual(uns('{"@qclass":"Infinity"}'), Infinity);
   t.deepEqual(uns('{"@qclass":"-Infinity"}'), -Infinity);
diff --git a/packages/same-structure/src/sameStructure.js b/packages/same-structure/src/sameStructure.js
index 5f6bd17dc11..23aadf74720 100644
--- a/packages/same-structure/src/sameStructure.js
+++ b/packages/same-structure/src/sameStructure.js
@@ -1,5 +1,5 @@
 import harden from '@agoric/harden';
-import { passStyleOf } from '@agoric/marshal';
+import { sameValueZero, passStyleOf } from '@agoric/marshal';
 import { assert, details, openDetail } from '@agoric/assert';
 
 // Shim of Object.fromEntries from
@@ -114,7 +114,7 @@ function sameStructure(left, right) {
     case 'symbol':
     case 'bigint':
     case 'presence': {
-      return Object.is(left, right);
+      return sameValueZero(left, right);
     }
     case 'copyRecord':
     case 'copyArray': {
@@ -193,7 +193,7 @@ function mustBeSameStructureInternal(left, right, message, path) {
     case 'symbol':
     case 'bigint':
     case 'presence': {
-      if (!Object.is(left, right)) {
+      if (!sameValueZero(left, right)) {
         complain('different');
       }
       break;