diff --git a/.github/workflows/bench.yml b/.github/workflows/bench.yml
index cf71465..af2b0c9 100644
--- a/.github/workflows/bench.yml
+++ b/.github/workflows/bench.yml
@@ -41,8 +41,10 @@ jobs:
       # The instrumented and PGO builds below use target-cpu=native, and
       # without --target cargo applies RUSTFLAGS to proc macros too. A cached
       # proc-macro .so compiled on a runner with a wider instruction set makes
-      # rustc die with SIGILL when it loads it, so the cache is keyed on the
-      # CPU model as well.
+      # rustc die with SIGILL when it loads it, so the CPU model is part of the
+      # cache key. It has to go in `shared-key`, not `key`: rust-cache appends
+      # `key` only when `shared-key` is unset, so setting both silently drops
+      # `key` from the cache key.
       - name: Read runner CPU model
         id: cpu
         run: echo "model=$(lscpu | sed -n 's/^Model name:[[:space:]]*//p' | tr -c 'A-Za-z0-9\n' '-')" >> "$GITHUB_OUTPUT"
@@ -51,8 +53,7 @@ jobs:
         uses: Swatinem/rust-cache@v2
         with:
           prefix-key: v1-bench
-          shared-key: x86_64-unknown-linux-gnu
-          key: ${{ steps.cpu.outputs.model }}
+          shared-key: x86_64-unknown-linux-gnu-${{ steps.cpu.outputs.model }}
 
       - name: Install dependencies
         run: mix deps.get