diff --git a/src/qlever-petrimaps/GeomCache.cpp b/src/qlever-petrimaps/GeomCache.cpp
index 21a3bf0..1aed61e 100644
--- a/src/qlever-petrimaps/GeomCache.cpp
+++ b/src/qlever-petrimaps/GeomCache.cpp
@@ -26,6 +26,9 @@ using util::geo::DPoint;
 using util::geo::FPoint;
 using util::geo::latLngToWebMerc;
 
+// change on each index-breaking change to the code base
+const static std::string INDEX_HASH_PREFIX = "_1_";
+
 // Different SPAQRL queries to obtain the WKT geometries from an endpoint.
 // It depends on the endpoint which query is used, see `getQuery`.
 //
@@ -1313,7 +1316,7 @@ std::string GeomCache::requestIndexHash() {
       return "";
     }
 
-    return response;
+    return INDEX_HASH_PREFIX + response;
   } else {
     LOG(ERROR) << "[GEOMCACHE] Failed to perform curl request for index hash.";
     return "";
diff --git a/src/qlever-petrimaps/Misc.h b/src/qlever-petrimaps/Misc.h
index e6f1e7a..9f66175 100644
--- a/src/qlever-petrimaps/Misc.h
+++ b/src/qlever-petrimaps/Misc.h
@@ -15,9 +15,8 @@
 #ifndef PETRIMAPS_MISC_H_
 #define PETRIMAPS_MISC_H_
 
-#define ID_TYPE uint32_t
-// #define QLEVER_ID_TYPE size_t
-#define QLEVER_ID_TYPE uint32_t
+#define ID_TYPE size_t
+#define QLEVER_ID_TYPE size_t
 
 const static ID_TYPE I_OFFSET = 500000000;
 const static size_t MAXROWS = 18446744073709551615u;