diff --git a/lib/spack/spack/repo.py b/lib/spack/spack/repo.py
index e4a945f0bfe..11419c2e4e6 100644
--- a/lib/spack/spack/repo.py
+++ b/lib/spack/spack/repo.py
@@ -599,7 +599,9 @@ def _build_index(self, name: str, indexer: Indexer):
         """Determine which packages need an update, and update indexes."""
 
         # Filename of the provider index cache (we assume they're all json)
-        cache_filename = f"{name}/{self.namespace}-index.json"
+        cache_filename = (
+            f"{name}/{self.namespace}-specfile_v{spack.spec.SPECFILE_FORMAT_VERSION}-index.json"
+        )
 
         # Compute which packages needs to be updated in the cache
         index_mtime = self.cache.mtime(cache_filename)