diff --git a/packages/quicktype-core/src/language/JavaScript/JavaScriptRenderer.ts b/packages/quicktype-core/src/language/JavaScript/JavaScriptRenderer.ts
index 63d5b5cd66..6186461959 100644
--- a/packages/quicktype-core/src/language/JavaScript/JavaScriptRenderer.ts
+++ b/packages/quicktype-core/src/language/JavaScript/JavaScriptRenderer.ts
@@ -445,10 +445,15 @@ ${hasArrayConstraints ? '        if ((typ.min !== undefined && val.length < typ.
         if (val === null) {
             return null;
         }
+        if (!(val instanceof Date) && (typeof val !== "string" || !/^[0-9]{4}-(?:0[1-9]|1[0-2])-(?:[0-2][0-9]|3[01])(?:T(?:[01][0-9]|2[0-3]):[0-5][0-9]:[0-5][0-9](?:[.][0-9]+)?(?:Z|[+-](?:[01][0-9]|2[0-3]):[0-5][0-9]))?$/i.test(val)))
+            return invalidValue(l("Date"), val, key, parent);
         const d = new Date(val);
         if (isNaN(d.valueOf())) {
             return invalidValue(l("Date"), val, key, parent);
         }
+        const date = typeof val === "string" ? val.slice(0, 10) : null;
+        if (date !== null && new Date(date + "T00:00:00Z").toISOString().slice(0, 10) !== date)
+            return invalidValue(l("Date"), val, key, parent);
         return d;
     }
 
diff --git a/packages/quicktype-core/src/language/JavaScriptPropTypes/JavaScriptPropTypesRenderer.ts b/packages/quicktype-core/src/language/JavaScriptPropTypes/JavaScriptPropTypesRenderer.ts
index 17b329a2d5..d03969986c 100644
--- a/packages/quicktype-core/src/language/JavaScriptPropTypes/JavaScriptPropTypesRenderer.ts
+++ b/packages/quicktype-core/src/language/JavaScriptPropTypes/JavaScriptPropTypesRenderer.ts
@@ -209,7 +209,7 @@ export class JavaScriptPropTypesRenderer extends ConvenienceRenderer {
                     return '(props, name) => props[name] == null || /^[0-9a-f]{8}-(?:[0-9a-f]{4}-){3}[0-9a-f]{12}$/i.test(props[name]) ? null : new Error("Expected UUID")';
                 }
                 if (transformedStringType.kind === "date-time") {
-                    return '(props, name) => props[name] == null || typeof props[name] === "string" && !Number.isNaN(Date.parse(props[name])) ? null : new Error("Expected date-time")';
+                    return '(props, name) => props[name] == null || typeof props[name] === "string" && /^(\\d{4}-(?:0[1-9]|1[0-2])-(?:[0-2]\\d|3[01]))(?:T(?:[01]\\d|2[0-3]):[0-5]\\d:[0-5]\\d(?:\\.\\d+)?(?:Z|[+-](?:[01]\\d|2[0-3]):[0-5]\\d))?$/i.test(props[name]) && !Number.isNaN(Date.parse(`${props[name].slice(0, 10)}T00:00:00Z`)) && new Date(Date.parse(`${props[name].slice(0, 10)}T00:00:00Z`)).toISOString().slice(0, 10) === props[name].slice(0, 10) ? null : new Error("Expected date-time")';
                 }
                 return "PropTypes.string";
             },
diff --git a/test/inputs/schema/date-time.8.fail.date-time.json b/test/inputs/schema/date-time.8.fail.date-time.json
new file mode 100644
index 0000000000..23a1d94a10
--- /dev/null
+++ b/test/inputs/schema/date-time.8.fail.date-time.json
@@ -0,0 +1,7 @@
+{
+  "date": "1985-04-12",
+  "time": "23:20:50.52Z",
+  "date-time": "1",
+  "union-array": ["1985-04-12", "23:20:50.52Z"],
+  "complex-union-array": ["2018-08-13T21:31:01+00:10", "foo", 123]
+}
diff --git a/test/unit/javascript-date-api.test.ts b/test/unit/javascript-date-api.test.ts
new file mode 100644
index 0000000000..f96c04e55d
--- /dev/null
+++ b/test/unit/javascript-date-api.test.ts
@@ -0,0 +1,42 @@
+import { InputData, JSONSchemaInput, quicktype } from "quicktype-core";
+import { expect, test } from "vitest";
+
+interface GeneratedConverters {
+    topLevelToJson: (value: { when: Date }) => string;
+}
+
+async function converters(): Promise<GeneratedConverters> {
+    const schemaInput = new JSONSchemaInput(undefined);
+    await schemaInput.addSource({
+        name: "TopLevel",
+        schema: JSON.stringify({
+            type: "object",
+            properties: {
+                when: { type: "string", format: "date-time" },
+            },
+            required: ["when"],
+        }),
+    });
+    const inputData = new InputData();
+    inputData.addInput(schemaInput);
+    const result = await quicktype({ inputData, lang: "javascript" });
+    const generatedModule: { exports: Partial<GeneratedConverters> } = {
+        exports: {},
+    };
+    new Function("exports", "module", result.lines.join("\n"))(
+        generatedModule.exports,
+        generatedModule,
+    );
+    return generatedModule.exports as GeneratedConverters;
+}
+
+test("JavaScript converter validates Date instances", async () => {
+    const { topLevelToJson } = await converters();
+
+    expect(
+        JSON.parse(topLevelToJson({ when: new Date("2024-02-29T00:00:00Z") })),
+    ).toEqual({ when: "2024-02-29T00:00:00.000Z" });
+    expect(() => topLevelToJson({ when: new Date(Number.NaN) })).toThrow(
+        "Expected Date",
+    );
+});