diff --git a/.changeset/yummy-meals-care.md b/.changeset/yummy-meals-care.md
new file mode 100644
index 000000000..9b57d66b0
--- /dev/null
+++ b/.changeset/yummy-meals-care.md
@@ -0,0 +1,5 @@
+---
+'@getodk/xpath': patch
+---
+
+Stringify NaN as an empty string according to the XForms specs.
diff --git a/packages/scenario/test/instance-input.test.ts b/packages/scenario/test/instance-input.test.ts
index 260b313f6..dca4aa90b 100644
--- a/packages/scenario/test/instance-input.test.ts
+++ b/packages/scenario/test/instance-input.test.ts
@@ -812,7 +812,7 @@ describe.each<InstanceRoundTripCase>([
 				readonly inner3: ComparableAnswer;
 			}
 
-			const NAN_ANSWER = stringAnswer(String(NaN));
+			const NAN_ANSWER = stringAnswer('');
 
 			interface MissingRepeatInstanceInputCase {
 				readonly detail: string;
diff --git a/packages/xforms-engine/test/instance/instance.test.ts b/packages/xforms-engine/test/instance/instance.test.ts
index 717039949..c3f55893b 100644
--- a/packages/xforms-engine/test/instance/instance.test.ts
+++ b/packages/xforms-engine/test/instance/instance.test.ts
@@ -133,7 +133,7 @@ describe('Form instance state', () => {
 
 		it.each([
 			{ firstValue: '2', expected: '4' },
-			{ firstValue: '', expected: 'NaN' },
+			{ firstValue: '', expected: '' },
 		])(
 			'updates the calculation to $expected when its dependency value is updated to $firstValue',
 			({ firstValue, expected }) => {
@@ -331,7 +331,7 @@ describe('Form instance state', () => {
 		it.each([
 			{ firstValue: '2', expected: '6' },
 			{ firstValue: '0', expected: '0' },
-			{ firstValue: '', expected: 'NaN' },
+			{ firstValue: '', expected: '' },
 		])(
 			'updates the calculated value $expected while it is relevant',
 			({ firstValue, expected }) => {
@@ -350,7 +350,7 @@ describe('Form instance state', () => {
 		it.each([
 			{ firstValue: '2', expected: '6' },
 			{ firstValue: '0', expected: '0' },
-			{ firstValue: '', expected: 'NaN' },
+			{ firstValue: '', expected: '' },
 		])(
 			'updates the calculated value $expected when it becomes relevant after the calculated dependency has been updated',
 			({ firstValue, expected }) => {
diff --git a/packages/xpath/src/evaluations/NumberEvaluation.ts b/packages/xpath/src/evaluations/NumberEvaluation.ts
index ea380951d..bc1ae43a3 100644
--- a/packages/xpath/src/evaluations/NumberEvaluation.ts
+++ b/packages/xpath/src/evaluations/NumberEvaluation.ts
@@ -18,6 +18,6 @@ export class NumberEvaluation<T extends XPathNode> extends ValueEvaluation<T, 'N
 
 		this.booleanValue = value !== 0 && !Number.isNaN(value);
 		this.numberValue = value;
-		this.stringValue = String(value);
+		this.stringValue = Number.isNaN(value) ? '' : String(value);
 	}
 }
diff --git a/packages/xpath/test/xforms/coalesce.test.ts b/packages/xpath/test/xforms/coalesce.test.ts
index c355342b3..11d71b583 100644
--- a/packages/xpath/test/xforms/coalesce.test.ts
+++ b/packages/xpath/test/xforms/coalesce.test.ts
@@ -40,6 +40,14 @@ describe('#coalesce()', () => {
 		testContext.assertStringValue('coalesce(/simple/xpath/to/node, "SECOND")', 'SECOND');
 	});
 
+	it('should return second value if first value is NaN', () => {
+		testContext.assertStringValue('coalesce(1 * /simple/xpath/to/node, "0")', '0');
+		testContext.assertStringValue(
+			'coalesce(/simple/xpath/to/node * /simple/xpath/to/node, "0")',
+			'0'
+		);
+	});
+
 	it('coalesce(self::*)', () => {
 		testContext = createXFormsTestContext(`
       <div id="FunctionSelectedCase">
diff --git a/packages/xpath/test/xforms/once.test.ts b/packages/xpath/test/xforms/once.test.ts
index 0b730561f..6308fa682 100644
--- a/packages/xpath/test/xforms/once.test.ts
+++ b/packages/xpath/test/xforms/once.test.ts
@@ -27,8 +27,8 @@ describe('once()', () => {
 			});
 		});
 
-		it('should set value to NaN', () => {
-			testContext.assertStringValue('once(. * 10)', 'NaN', {
+		it('should set value to empty string when arithmetic on empty node produces NaN', () => {
+			testContext.assertStringValue('once(. * 10)', '', {
 				contextNode,
 			});
 		});
diff --git a/packages/xpath/test/xforms/randomize.test.ts b/packages/xpath/test/xforms/randomize.test.ts
index a45b74877..1fe2a43e3 100644
--- a/packages/xpath/test/xforms/randomize.test.ts
+++ b/packages/xpath/test/xforms/randomize.test.ts
@@ -80,7 +80,7 @@ describe('randomize()', () => {
 			{ seed: 0, expected: 'CBEAFD' },
 			{ seed: NaN, expected: 'CBEAFD' },
 			{ seed: Infinity, expected: 'CBEAFD' },
-			{ seed: -Infinity, expected: 'CFBEAD' },
+			{ seed: -Infinity, expected: 'CBEAFD' },
 			{ seed: 'floor(1.1)', expected: 'BFEACD' },
 			{ seed: '//xhtml:div[@id="testFunctionNodeset2"]/xhtml:p', expected: 'BFEACD' },
 			{ seed: MIRROR_HASH_VALUE, expected: MIRROR_HASH_SORT_ORDER },