diff --git a/airflow-core/docs/authoring-and-scheduling/language-sdks/java.rst b/airflow-core/docs/authoring-and-scheduling/language-sdks/java.rst
index c8b73b4626a28..703675412ec76 100644
--- a/airflow-core/docs/authoring-and-scheduling/language-sdks/java.rst
+++ b/airflow-core/docs/authoring-and-scheduling/language-sdks/java.rst
@@ -426,6 +426,14 @@ represented as Java objects when read back via ``getXCom``.
      - object
      - ``Map<String, Object>``
 
+.. note::
+
+   ``char`` and ``Character`` are not supported.  JSON has no single-character type, so a
+   character value is stored as a JSON string (or a number) and is read back as one of the
+   Java types in the table above.  Declaring ``char`` or ``Character`` as an
+   ``@Builder.XCom`` parameter compiles, but reading a pushed value fails at runtime with a
+   ``ClassCastException``.  Use ``String`` instead.
+
 .. note::
 
    An ``@Builder.XCom`` parameter that reads a value which was never pushed resolves to