diff --git a/core/misc/singleton/singleton_manager.cpp b/core/misc/singleton/singleton_manager.cpp
index 3dec94a..08ffad0 100644
--- a/core/misc/singleton/singleton_manager.cpp
+++ b/core/misc/singleton/singleton_manager.cpp
@@ -49,14 +49,14 @@ void singleton_manager::init() {
 void singleton_manager::release() const {
     {
         singleton_release_guard release_guard(true);
-        for (int32_t j = singletons_.size() - 1; j >= 0; --j) {
+        for (int32_t j = static_cast<int32_t>(singletons_.size()) - 1; j >= 0; --j) {
             const auto s = singletons_[j];
             release_guard.release_singleton(s);
         }
     }
     {
         singleton_release_guard release_guard(false);
-        for (int32_t j = singletons_.size() - 1; j >= 0; --j) {
+        for (int32_t j = static_cast<int32_t>(singletons_.size()) - 1; j >= 0; --j) {
             const auto s = singletons_[j];
             release_guard.release_singleton(s);
         }