diff --git a/src/signal.cpp b/src/signal.cpp
index d53fc3d4a7..3ac77872f8 100644
--- a/src/signal.cpp
+++ b/src/signal.cpp
@@ -1766,6 +1766,8 @@ static bool RemapNewSignalStyles(const std::array<NewSignalStyleMapping, MAX_NEW
 
 static void DetermineSignalStyleMapping(std::array<NewSignalStyleMapping, MAX_NEW_SIGNAL_STYLES> &mapping)
 {
+	mapping.fill({});
+
 	for (uint i = 0; i < _num_new_signal_styles; i++) {
 		mapping[i].grfid = _new_signal_styles[i].grffile->grfid;
 		mapping[i].grf_local_id = _new_signal_styles[i].grf_local_id;
diff --git a/src/sl/newsignals_sl.cpp b/src/sl/newsignals_sl.cpp
index 620be20948..546911d6a7 100644
--- a/src/sl/newsignals_sl.cpp
+++ b/src/sl/newsignals_sl.cpp
@@ -26,6 +26,8 @@ static void Save_NSID()
 
 static void Load_NSID()
 {
+	_new_signal_style_mapping.fill({});
+
 	uint count = SlReadUint32();
 	for (uint i = 0; i < count; i++) {
 		NewSignalStyleMapping mapping;