diff --git a/docs/book/src/contributing/style.md b/docs/book/src/contributing/style.md
index fe09fb6c2f..0c58a83a1d 100644
--- a/docs/book/src/contributing/style.md
+++ b/docs/book/src/contributing/style.md
@@ -236,22 +236,6 @@ In the "Good" version, the precondition check and usage are checked in the same
 
 **Rationale:** non-local code properties degrade under change.
 
-When checking a boolean precondition, prefer `if !invariant` to `if negated_invariant`:
-
-```rust
-// GOOD
-if !(idx < len) {
-    return None;
-}
-
-// BAD
-if idx >= len {
-    return None;
-}
-```
-
-**Rationale:** it's useful to see the invariant relied upon by the rest of the function clearly spelled out.
-
 ## Control Flow
 
 As a special case of the previous rule, do not hide control flow inside functions, push it to the caller: