diff --git a/packages/xsnap/src/xsnap.c b/packages/xsnap/src/xsnap.c
index 27cc843ff0f9..cbc501cd8dcf 100644
--- a/packages/xsnap/src/xsnap.c
+++ b/packages/xsnap/src/xsnap.c
@@ -204,19 +204,7 @@ int main(int argc, char* argv[])
 	int error = 0;
 	int interval = 0;
 	int freeze = 0;
-	xsCreation _creation = {
-		16 * 1024 * 1024,	/* initialChunkSize */
-		16 * 1024 * 1024,	/* incrementalChunkSize */
-		1 * 1024 * 1024,	/* initialHeapCount */
-		1 * 1024 * 1024,	/* incrementalHeapCount */
-		4096,				/* stackCount */
-		32000,				/* keyCount */
-		1993,				/* nameModulo */
-		127,				/* symbolModulo */
-		8192 * 1024,		/* parserBufferSize */
-		1993,				/* parserTableModulo */
-	};
-	xsCreation* creation = &_creation;
+	int parserBufferSize = 8192 * 1024;
 
 	txSnapshot snapshot = {
 		SNAPSHOT_SIGNATURE,
@@ -279,6 +267,15 @@ int main(int argc, char* argv[])
 				return 1;
 			}
 		}
+		else if (!strcmp(argv[argi], "-s")) {
+			argi++;
+			if (argi < argc)
+				parserBufferSize = 1024 * atoi(argv[argi]);
+			else {
+				fxPrintUsage();
+				return 1;
+			}
+		}
 		else if (!strcmp(argv[argi], "-v")) {
 			printf("xsnap %s (XS %d.%d.%d)\n", XSNAP_VERSION, XS_MAJOR_VERSION, XS_MINOR_VERSION, XS_PATCH_VERSION);
 			return 0;
@@ -287,6 +284,21 @@ int main(int argc, char* argv[])
 			return 1;
 		}
 	}
+	fprintf(stderr, "@@parserBufferSize %d", parserBufferSize);
+	xsCreation _creation = {
+		16 * 1024 * 1024,	/* initialChunkSize */
+		16 * 1024 * 1024,	/* incrementalChunkSize */
+		1 * 1024 * 1024,	/* initialHeapCount */
+		1 * 1024 * 1024,	/* incrementalHeapCount */
+		4096,				/* stackCount */
+		32000,				/* keyCount */
+		1993,				/* nameModulo */
+		127,				/* symbolModulo */
+		parserBufferSize,	/* parserBufferSize */
+		1993,				/* parserTableModulo */
+	};
+	xsCreation* creation = &_creation;
+
 	if (gxCrankMeteringLimit) {
 		if (interval == 0)
 			interval = 1;
@@ -850,11 +862,12 @@ void fxPatchBuiltIns(txMachine* machine)
 
 void fxPrintUsage()
 {
-	printf("xsnap [-h] [-f] [-i <interval>] [-l <limit>] [-m] [-r <snapshot>] [-s] [-v]\n");
+	printf("xsnap [-h] [-f] [-i <interval>] [-l <limit>] [-s <size>] [-m] [-r <snapshot>] [-s] [-v]\n");
 	printf("\t-f: freeze the XS machine\n");
 	printf("\t-h: print this help message\n");
 	printf("\t-i <interval>: metering interval (default to 1)\n");
 	printf("\t-l <limit>: metering limit (default to none)\n");
+	printf("\t-s <size>: parser buffer size, in kB (default to 8192)\n");
 	printf("\t-r <snapshot>: read snapshot to create the XS machine\n");
 	printf("\t-v: print XS version\n");
 }
diff --git a/packages/xsnap/src/xsnap.js b/packages/xsnap/src/xsnap.js
index b82b62226c72..5cf0c48683f3 100644
--- a/packages/xsnap/src/xsnap.js
+++ b/packages/xsnap/src/xsnap.js
@@ -46,6 +46,7 @@ function echoCommand(arg) {
  * @param {(request:Uint8Array) => Promise<Uint8Array>} [options.handleCommand]
  * @param {string=} [options.name]
  * @param {boolean=} [options.debug]
+ * @param {number=} [options.parserBufferSize] in kB (must be an integer)
  * @param {string=} [options.snapshot]
  * @param {'ignore' | 'inherit'} [options.stdout]
  * @param {'ignore' | 'inherit'} [options.stderr]
@@ -58,6 +59,7 @@ export function xsnap(options) {
     name = '<unnamed xsnap worker>',
     handleCommand = echoCommand,
     debug = false,
+    parserBufferSize = undefined,
     snapshot = undefined,
     stdout = 'ignore',
     stderr = 'ignore',
@@ -82,10 +84,16 @@ export function xsnap(options) {
   /** @type {Deferred<void>} */
   const vatExit = defer();
 
-  const args = snapshot ? ['-r', snapshot] : [];
+  const args = [];
+  if (snapshot) {
+    args.push('-r', snapshot);
+  }
   if (meteringLimit) {
     args.push('-l', `${meteringLimit}`);
   }
+  if (parserBufferSize) {
+    args.push('-s', `${parserBufferSize}`);
+  }
 
   const xsnapProcess = spawn(bin, args, {
     stdio: ['ignore', stdout, stderr, 'pipe', 'pipe'],
diff --git a/packages/xsnap/test/test-xsnap.js b/packages/xsnap/test/test-xsnap.js
index e3b3d163849c..49086b90dba4 100644
--- a/packages/xsnap/test/test-xsnap.js
+++ b/packages/xsnap/test/test-xsnap.js
@@ -435,50 +435,40 @@ test('property name space exhaustion: orderly fail-stop', async t => {
   }
 });
 
-test('parser buffer exhaustion: orderly fail-stop', async t => {
-  const grow = `
-  const send = it => issueCommand(ArrayBuffer.fromString(it));
-  let expr = '1+1';
+(() => {
+  const grow = qty => `
+  const send = it => issueCommand(ArrayBuffer.fromString(JSON.stringify(it)));
+  let expr = \`"\${Array(${qty}).fill('abcd').join('')}"\`;
   try {
-    for(;;) {
-      send(expr.length);
-      eval(expr);
-      expr = expr + ',' + expr;
-    }
+    eval(expr);
+    send(expr.length);
   } catch (err) {
-    // buffer exhaustion should not be catchable!
     send(err.message);
   }
   `;
   for (const debug of [false, true]) {
-    const opts = options();
-    const vat = xsnap({ ...opts, debug });
-    t.teardown(() => vat.terminate());
-    // eslint-disable-next-line no-await-in-loop
-    await t.throwsAsync(vat.evaluate(grow), { message: /exited with code 7$/ });
-    t.deepEqual(opts.messages.slice(0, 19), [
-      '3',
-      '7',
-      '15',
-      '31',
-      '63',
-      '127',
-      '255',
-      '511',
-      '1023',
-      '2047',
-      '4095',
-      '8191',
-      '16383',
-      '32767',
-      '65535',
-      '131071',
-      '262143',
-      '524287',
-      '1048575',
-    ]);
+    for (const [parserBufferSize, qty, failure] of [
+      [undefined, 100, null],
+      [undefined, 8192 * 1024 + 100, 'buffer overflow'],
+      [2, 10, null],
+      [2, 50000, 'buffer overflow'],
+    ]) {
+      test(`parser buffer size ${parserBufferSize ||
+        'default'}k; rep ${qty}; debug ${debug}`, async t => {
+        const opts = options();
+        const vat = xsnap({ ...opts, debug, parserBufferSize });
+        t.teardown(() => vat.terminate());
+        const expected = failure ? [failure] : [qty * 4 + 2];
+        // eslint-disable-next-line no-await-in-loop
+        await t.notThrowsAsync(vat.evaluate(grow(qty)));
+        t.deepEqual(
+          expected,
+          opts.messages.map(txt => JSON.parse(txt)),
+        );
+      });
+    }
   }
-});
+})();
 
 (() => {
   const challenges = [