diff --git a/.github/workflows/semantic-index.yml b/.github/workflows/semantic-index.yml
index c1365e3..da12d05 100644
--- a/.github/workflows/semantic-index.yml
+++ b/.github/workflows/semantic-index.yml
@@ -63,7 +63,7 @@ jobs:
 
       # Cache the ONNX model weights between runs (miss -> downloaded from HF).
       - name: Cache embedding model
-        uses: actions/cache@v4
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
         with:
           path: ~/.cache/semantic-model
           key: semantic-model-minilm-v1