diff -ru dhtnet.orig/src/upnp/upnp_context.cpp dhtnet/src/upnp/upnp_context.cpp
--- dhtnet.orig/src/upnp/upnp_context.cpp	2025-10-04 15:51:40.889482196 +0200
+++ dhtnet/src/upnp/upnp_context.cpp	2025-10-04 16:09:31.538008243 +0200
@@ -734,9 +734,12 @@
     }
     if (toRenewLaterCount > 0) {
         nextRenewalTime += MAPPING_RENEWAL_THROTTLING_DELAY;
-        if (logger_) logger_->debug("{} mapping(s) didn't need to be renewed (next renewal scheduled for {:%Y-%m-%d %H:%M:%S})",
+        if (logger_) {
+            std::time_t t = sys_clock::to_time_t(nextRenewalTime);
+            logger_->debug("{} mapping(s) didn't need to be renewed (next renewal scheduled for {:%Y-%m-%d %H:%M:%S})",
                                     toRenewLaterCount,
-                                    fmt::localtime(sys_clock::to_time_t(nextRenewalTime)));
+                                    *std::localtime(&t));
+        }
         mappingRenewalTimer_.expires_at(nextRenewalTime);
         mappingRenewalTimer_.async_wait([this](asio::error_code const& ec) {
             if (ec != asio::error::operation_aborted)
@@ -783,8 +786,11 @@
     if (nextRenewalTime == mappingRenewalTimer_.expiry())
         return;
 
-    if (logger_) logger_->debug("Scheduling next port mapping renewal for {:%Y-%m-%d %H:%M:%S}",
-                                 fmt::localtime(sys_clock::to_time_t(nextRenewalTime)));
+    if (logger_) {
+        std::time_t t = sys_clock::to_time_t(nextRenewalTime);
+        logger_->debug("Scheduling next port mapping renewal for {:%Y-%m-%d %H:%M:%S}",
+                                *std::localtime(&t));
+    }
     mappingRenewalTimer_.expires_at(nextRenewalTime);
     mappingRenewalTimer_.async_wait([this](asio::error_code const& ec) {
         if (ec != asio::error::operation_aborted)