diff --git a/Externals/rangeset/include/rangeset/rangeset.h b/Externals/rangeset/include/rangeset/rangeset.h
index 6933c67f5b..60f665c9ee 100644
--- a/Externals/rangeset/include/rangeset/rangeset.h
+++ b/Externals/rangeset/include/rangeset/rangeset.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <cassert>
+#include <cstddef>
 #include <map>
 
 namespace HyoutaUtilities {
@@ -217,7 +218,7 @@ public:
     return get_from(it) <= value && value < get_to(it);
   }
 
-  size_t size() const {
+  std::size_t size() const {
     return Map.size();
   }
 
diff --git a/Externals/rangeset/include/rangeset/rangesizeset.h b/Externals/rangeset/include/rangeset/rangesizeset.h
index 8519209863..e91c74f210 100644
--- a/Externals/rangeset/include/rangeset/rangesizeset.h
+++ b/Externals/rangeset/include/rangeset/rangesizeset.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <cassert>
+#include <cstddef>
 #include <map>
 #include <type_traits>
 
@@ -322,7 +323,7 @@ public:
     return get_from(it) <= value && value < get_to(it);
   }
 
-  size_t size() const {
+  std::size_t size() const {
     return Map.size();
   }
 
@@ -330,7 +331,7 @@ public:
     return Map.empty();
   }
 
-  size_t by_size_count(const SizeT& key) const {
+  std::size_t by_size_count(const SizeT& key) const {
     return Sizes.count(key);
   }