diff --git a/action.yml b/action.yml
index 656c2b14..21e1bc8d 100644
--- a/action.yml
+++ b/action.yml
@@ -98,9 +98,11 @@ runs:
       shell: bash
 
     - run: |
-        : enable Cargo sparse registry  # ignored by stable cargo
-        if [ -z ${CARGO_UNSTABLE_SPARSE_REGISTRY+set} ]; then
-          echo CARGO_UNSTABLE_SPARSE_REGISTRY=true >> $GITHUB_ENV
+        : enable Cargo sparse registry  # except on 1.66 and 1.67, on which it is unstable
+        if [ -z ${CARGO_REGISTRIES_CRATES_IO_PROTOCOL+set} ] \
+          && ! rustc +${{steps.parse.outputs.toolchain}} --version --verbose | grep -q '^release: 1\.6[67]\.'
+        then
+          echo CARGO_REGISTRIES_CRATES_IO_PROTOCOL=sparse >> $GITHUB_ENV
         fi
       shell: bash