diff --git a/highfive/configs/rust-lang/rust.json b/highfive/configs/rust-lang/rust.json
index f6e8eb76..d94c17ce 100644
--- a/highfive/configs/rust-lang/rust.json
+++ b/highfive/configs/rust-lang/rust.json
@@ -133,6 +133,10 @@
         "src/tools/tidy":                        ["@Mark-Simulacrum"]
     },
     "mentions": {
+        "library/portable-simd": {
+            "message": "library/portable-simd is a subtree of https://github.com/rust-lang/portable-simd and changes here will have to be cherry-picked upstream.",
+            "reviewers": ["@rust-lang/project-portable-simd"]
+        },
         "src/rustdoc-json-types": {
           "message": "rustdoc-json-types is a **public** (although nightly-only) API. If possible, consider changing `src/librustdoc/json/conversions.rs`; otherwise, make sure you bump the `FORMAT_VERSION` constant.",
           "reviewers": ["@CraftSpider", "@aDotInTheVoid"]