diff --git a/lix/libstore/binary-cache-store.cc b/lix/libstore/binary-cache-store.cc
index d9487f5b0..dde94acd0 100644
--- a/lix/libstore/binary-cache-store.cc
+++ b/lix/libstore/binary-cache-store.cc
@@ -190,6 +190,7 @@ try {
 
         auto * buildIdDir = std::get_if<nar_index::Directory>(&narIndex);
         for (auto subdir : { "lib", "debug", ".build-id" }) {
+            if (!buildIdDir) break;
             // get returns nullptr subdir does not exist, and std::get_if propagates it.
             buildIdDir = std::get_if<nar_index::Directory>(get(buildIdDir->contents, subdir));
         }