diff --git a/style-guide.md b/style-guide.md
index 6cf5f4589b..17e9fe9797 100644
--- a/style-guide.md
+++ b/style-guide.md
@@ -10,7 +10,27 @@ the exceptions in this file trump them both.
 [chr-style]: https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md
 [goog-style]: https://google.github.io/styleguide/cppguide.html
 
+Some older parts of the code violate the style guide in various ways.
+
+* If making small changes to such code, follow the style guide when
+  it’s reasonable to do so, but in matters of formatting etc., it is
+  often better to be consistent with the surrounding code.
+* If making large changes to such code, consider first cleaning it up
+  in a separate CL.
+
 ### Exceptions
 
 There are no exceptions yet. If and when exceptions are adopted,
-they'll be listed here.
+they’ll be listed here.
+
+## C
+
+There’s a substantial chunk of legacy C code in WebRTC, and a lot of
+it is old enough that it violates the parts of the C++ style guide
+that also applies to C (naming etc.) for the simple reason that it
+pre-dates the use of the current C++ style guide for this code base.
+
+* If making small changes to C code, mimic the style of the
+  surrounding code.
+* If making large changes to C code, consider converting the whole
+  thing to C++ first.