diff --git a/.changeset/twenty-dolphins-check.md b/.changeset/twenty-dolphins-check.md
new file mode 100644
index 000000000..4e9d78e8e
--- /dev/null
+++ b/.changeset/twenty-dolphins-check.md
@@ -0,0 +1,5 @@
+---
+'@keystatic/core': patch
+---
+
+Fix serializing conditional fields in content components in `fields.markdoc` where the value is `undefined`
diff --git a/packages/keystatic/src/form/fields/markdoc/editor/tests/markdoc.test.tsx b/packages/keystatic/src/form/fields/markdoc/editor/tests/markdoc.test.tsx
index 901f7980b..a794f3c61 100644
--- a/packages/keystatic/src/form/fields/markdoc/editor/tests/markdoc.test.tsx
+++ b/packages/keystatic/src/form/fields/markdoc/editor/tests/markdoc.test.tsx
@@ -43,6 +43,18 @@ const schema = createEditorSchema(
         something: fields.text({ label: 'Something' }),
       },
     }),
+    'string-directly-in-conditional': block({
+      label: 'String directly in conditional',
+      schema: {
+        conditional: fields.conditional(
+          fields.checkbox({ label: 'Checkbox' }),
+          {
+            true: fields.text({ label: 'True' }),
+            false: fields.text({ label: 'False' }),
+          }
+        ),
+      },
+    }),
   },
   false
 );
@@ -651,3 +663,30 @@ test('only inline in list item', () => {
     "
   `);
 });
+
+test('undefined in conditional value', () => {
+  const markdoc = `{% string-directly-in-conditional conditional={discriminant:false} /%}`;
+  const editor = fromMarkdoc(markdoc);
+  expect(editor).toMatchInlineSnapshot(`
+    <doc>
+      <node_selection>
+        <string-directly-in-conditional
+          props={
+            {
+              "extraFiles": [],
+              "value": {
+                "conditional": {
+                  "discriminant": false,
+                },
+              },
+            }
+          }
+        />
+      </node_selection>
+    </doc>
+  `);
+  expect(toMarkdoc(editor)).toMatchInlineSnapshot(`
+    "{% string-directly-in-conditional conditional={discriminant: false} /%}
+    "
+  `);
+});
diff --git a/packages/keystatic/src/form/serialize-props.ts b/packages/keystatic/src/form/serialize-props.ts
index 8dc52797f..0b9002e64 100644
--- a/packages/keystatic/src/form/serialize-props.ts
+++ b/packages/keystatic/src/form/serialize-props.ts
@@ -95,6 +95,12 @@ export function serializeProps(
       array(_schema, value) {
         return value.map(val => (val === undefined ? null : val));
       },
+      conditional(_schema, value) {
+        if (value.value === undefined) {
+          return { discriminant: value.discriminant } as any;
+        }
+        return value;
+      },
       child() {
         return undefined as any;
       },