diff --git a/util/probing_hash_table.hh b/util/probing_hash_table.hh
index 438de92fb..18cae85cd 100644
--- a/util/probing_hash_table.hh
+++ b/util/probing_hash_table.hh
@@ -30,7 +30,7 @@ class DivMod {
   public:
     explicit DivMod(std::size_t buckets) : buckets_(buckets) {}
 
-    static std::size_t RoundBuckets(std::size_t from) {
+    static std::uint64_t RoundBuckets(std::uint64_t from) {
       return from;
     }
 
@@ -58,7 +58,7 @@ class Power2Mod {
     }
 
     // Round up to next power of 2.
-    static std::size_t RoundBuckets(std::size_t from) {
+    static std::uint64_t RoundBuckets(std::uint64_t from) {
       --from;
       from |= from >> 1;
       from |= from >> 2;