diff --git a/README.md b/README.md
index a5f7dcc..f646876 100644
--- a/README.md
+++ b/README.md
@@ -58,4 +58,4 @@ Currently the format string supports the following special sequences:
 ```
 
 ### Limitations
-There is no compile-time warning if the number of {}'s in the format string doesn't match the number of return values.  You'll just get None for extra return values.  See src/lib.rs for more details.
+There is no compile-time warning if the number of {}'s in the format string doesn't match the number of return values.  You'll just get None for extra return values.  See src/lib.rs for more details. Also, a trailing comma at the end of the macro invocation is treated as an undeclared type.
diff --git a/src/lib.rs b/src/lib.rs
index a64ac00..5f34470 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -85,8 +85,10 @@
 //!
 //! ## LIMITATIONS:
 //! There are no compile-time checks to make sure the format
-//! strings matches the number of return arguments.  Extra
-//! return values will be None or cause a Result error.
+//! strings matches the number of return arguments. Also, a
+//! trailing comma at the end of the macro invocation is
+//! treated as an undeclared type. Extra return values will
+//! be None or cause a Result error.
 //!
 //! Like sscanf(), whitespace (including \n) is largely ignored.
 //!