diff --git a/src/diagnostics.md b/src/diagnostics.md
index 5b6d1323f..ddcaa8f33 100644
--- a/src/diagnostics.md
+++ b/src/diagnostics.md
@@ -156,6 +156,8 @@ use an error-level lint instead of a fixed error.
   compiler messages are an important learning tool.
 - When talking about the compiler, call it `the compiler`, not `Rust` or
   `rustc`.
+- Use the [Oxford comma](https://en.wikipedia.org/wiki/Serial_comma) when
+  writing lists of items.
 
 ### Lint naming