diff --git a/peps/pep-0007.rst b/peps/pep-0007.rst
index 7db059debc68..fd7b48218b87 100644
--- a/peps/pep-0007.rst
+++ b/peps/pep-0007.rst
@@ -34,6 +34,10 @@ C dialect
 
 * The public C API should be compatible with C99 and with C++03.
 
+  The existing API does use a few C11 features which are
+  commonly available as compiler extensions to C99.
+  New API should not use these features.
+
 * Python 3.6 to 3.10 use C89 with several select C99 features:
 
   - Standard integer types in ``<stdint.h>`` and ``<inttypes.h>``. We