diff --git a/Code/GraphMol/SynthonSpaceSearch/SearchResults.cpp b/Code/GraphMol/SynthonSpaceSearch/SearchResults.cpp
index dc983fc86..a8f923622 100644
--- a/Code/GraphMol/SynthonSpaceSearch/SearchResults.cpp
+++ b/Code/GraphMol/SynthonSpaceSearch/SearchResults.cpp
@@ -12,7 +12,7 @@
 
 namespace RDKit::SynthonSpaceSearch {
 SearchResults::SearchResults(std::vector<std::unique_ptr<ROMol>> &&mols,
-                             const size_t maxNumRes, bool timedOut,
+                             const std::uint64_t maxNumRes, bool timedOut,
                              bool cancelled)
     : d_maxNumResults(maxNumRes), d_timedOut(timedOut), d_cancelled(cancelled) {
   d_hitMolecules = std::move(mols);
diff --git a/Code/GraphMol/SynthonSpaceSearch/SearchResults.h b/Code/GraphMol/SynthonSpaceSearch/SearchResults.h
index 03842f842..75c921c2e 100644
--- a/Code/GraphMol/SynthonSpaceSearch/SearchResults.h
+++ b/Code/GraphMol/SynthonSpaceSearch/SearchResults.h
@@ -22,7 +22,7 @@ namespace RDKit::SynthonSpaceSearch {
 class RDKIT_SYNTHONSPACESEARCH_EXPORT SearchResults {
  public:
   explicit SearchResults() : d_maxNumResults(0) {}
-  SearchResults(std::vector<std::unique_ptr<ROMol>> &&mols, size_t maxNumRes,
+  SearchResults(std::vector<std::unique_ptr<ROMol>> &&mols, std::uint64_t maxNumRes,
                 bool timedOut, bool cancelled);
   SearchResults(const SearchResults &other);
   SearchResults(SearchResults &&other) = default;
@@ -39,7 +39,7 @@ class RDKIT_SYNTHONSPACESEARCH_EXPORT SearchResults {
    *
    * @return int
    */
-  size_t getMaxNumResults() const { return d_maxNumResults; }
+  std::uint64_t getMaxNumResults() const { return d_maxNumResults; }
   /*!
    * Returns the hit molecules from the search. Not necessarily all
    * those possible, just the maximum number requested.
@@ -71,7 +71,7 @@ class RDKIT_SYNTHONSPACESEARCH_EXPORT SearchResults {
   // filled in then if needed, empty otherwise.
   std::unordered_set<std::string> d_molNames;
 
-  size_t d_maxNumResults;
+  std::uint64_t d_maxNumResults;
   bool d_timedOut{false};
   bool d_cancelled{false};
 };
diff --git a/Code/GraphMol/SynthonSpaceSearch/SynthonSpaceSearcher.cpp b/Code/GraphMol/SynthonSpaceSearch/SynthonSpaceSearcher.cpp
index 19ddd0d9f..7bf819ea8 100644
--- a/Code/GraphMol/SynthonSpaceSearch/SynthonSpaceSearcher.cpp
+++ b/Code/GraphMol/SynthonSpaceSearch/SynthonSpaceSearcher.cpp
@@ -61,12 +61,12 @@ SearchResults SynthonSpaceSearcher::search() {
       d_query, getSpace().getMaxNumSynthons(), d_params.maxNumFragSets, endTime,
       d_params.numThreads, timedOut);
   if (timedOut || ControlCHandler::getGotSignal()) {
-    return SearchResults{std::move(results), 0UL, timedOut,
+    return SearchResults{std::move(results), 0ULL, timedOut,
                          ControlCHandler::getGotSignal()};
   }
   extraSearchSetup(fragments);
   if (ControlCHandler::getGotSignal()) {
-    return SearchResults{std::move(results), 0UL, timedOut, true};
+    return SearchResults{std::move(results), 0ULL, timedOut, true};
   }
 
   std::uint64_t totHits = 0;