diff --git a/src/generateClient.spec.ts b/src/generateClient.spec.ts
index ed6b528f..7429febb 100644
--- a/src/generateClient.spec.ts
+++ b/src/generateClient.spec.ts
@@ -211,6 +211,11 @@ test('generateClientSource: string enum exports emit const object and derived ty
 } as const;`),
         true,
     );
+    assert.equal(
+        generated.includes('issueStatus: p.union([p.literal("open"), p.literal("closed"), p.literal("ignored")], \'invalid\'),'),
+        true,
+        'string enum exports must use runtyp 2 p.union([...], message) syntax',
+    );
     assert.equal(
         generated.includes('export type IssueStatus = (typeof IssueStatus)[keyof typeof IssueStatus];'),
         true,
diff --git a/src/generateValidators.spec.ts b/src/generateValidators.spec.ts
index b84536b9..2cbd9fda 100644
--- a/src/generateValidators.spec.ts
+++ b/src/generateValidators.spec.ts
@@ -33,7 +33,21 @@ test('schemaToRuntyp: union via oneOf', (assert) => {
         ],
     });
 
-    assert.equal(expr, 'p.union(p.string(), p.number())');
+    assert.equal(expr, 'p.union([p.string(), p.number()], \'invalid\')');
+
+});
+
+test('schemaToRuntyp: string enum uses runtyp 2 union syntax', (assert) => {
+
+    const expr = schemaToRuntyp({
+        type: 'string',
+        enum: ['open', 'closed'],
+    });
+
+    assert.equal(
+        expr,
+        'p.union([p.literal("open"), p.literal("closed")], \'invalid\')',
+    );
 
 });
 
diff --git a/src/generateValidators/schemaToRuntyp.ts b/src/generateValidators/schemaToRuntyp.ts
index da0f1f52..f9205877 100644
--- a/src/generateValidators/schemaToRuntyp.ts
+++ b/src/generateValidators/schemaToRuntyp.ts
@@ -12,6 +12,12 @@ function escapeString(value: string): string {
 
 }
 
+function unionExpr(parts: string[]): string {
+
+    return `p.union([${parts.join(', ')}], 'invalid')`;
+
+}
+
 function schemaToRuntypExpr(schema: unknown): string {
 
     if (!isRecord(schema)) {
@@ -32,7 +38,7 @@ function schemaToRuntypExpr(schema: unknown): string {
 
         if (literals.length === 1) return literals[0];
 
-        return `p.union(${literals.join(', ')})`;
+        return unionExpr(literals);
 
     }
 
@@ -48,7 +54,7 @@ function schemaToRuntypExpr(schema: unknown): string {
 
         if (parts.length === 1) return parts[0];
 
-        return `p.union(${parts.join(', ')})`;
+        return unionExpr(parts);
 
     }
 
@@ -58,7 +64,7 @@ function schemaToRuntypExpr(schema: unknown): string {
 
         if (parts.length === 1) return parts[0];
 
-        return `p.union(${parts.join(', ')})`;
+        return unionExpr(parts);
 
     }