diff --git a/src/newgrf_debug_gui.cpp b/src/newgrf_debug_gui.cpp
--- a/src/newgrf_debug_gui.cpp
+++ b/src/newgrf_debug_gui.cpp
@@ -503,7 +503,7 @@ struct NewGRFInspectWindow : Window {
 						break;
 
 					case NIT_CARGO:
-						string = value != INVALID_CARGO ? CargoSpec::Get(value)->name : STR_QUANTITY_N_A;
+						string = IsValidCargoID(value) ? CargoSpec::Get(value)->name : STR_QUANTITY_N_A;
 						break;
 
 					default: