diff --git a/src/os/os2/os2.cpp b/src/os/os2/os2.cpp
index eb3671029d..386cc4dbb7 100644
--- a/src/os/os2/os2.cpp
+++ b/src/os/os2/os2.cpp
@@ -174,6 +174,9 @@ int CDECL main(int argc, char *argv[])
 {
 	SetRandomSeed(time(NULL));
 
+	/* Make sure our arguments contain only valid UTF-8 characters. */
+	for (int i = 0; i < argc; i++) ValidateString(argv[i]);
+
 	return openttd_main(argc, argv);
 }
 
diff --git a/src/os/unix/unix.cpp b/src/os/unix/unix.cpp
index 59d40cc89f..24dedb2ee1 100644
--- a/src/os/unix/unix.cpp
+++ b/src/os/unix/unix.cpp
@@ -259,7 +259,8 @@ void cocoaReleaseAutoreleasePool();
 
 int CDECL main(int argc, char *argv[])
 {
-	int ret;
+	/* Make sure our arguments contain only valid UTF-8 characters. */
+	for (int i = 0; i < argc; i++) ValidateString(argv[i]);
 
 #ifdef WITH_COCOA
 	cocoaSetupAutoreleasePool();
@@ -275,7 +276,7 @@ int CDECL main(int argc, char *argv[])
 
 	signal(SIGPIPE, SIG_IGN);
 
-	ret = openttd_main(argc, argv);
+	int ret = openttd_main(argc, argv);
 
 #ifdef WITH_COCOA
 	cocoaReleaseAutoreleasePool();
diff --git a/src/os/windows/win32.cpp b/src/os/windows/win32.cpp
index 3d5f0ebde5..f69f01f6cb 100644
--- a/src/os/windows/win32.cpp
+++ b/src/os/windows/win32.cpp
@@ -453,6 +453,9 @@ int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLi
 
 	argc = ParseCommandLine(cmdline, argv, lengthof(argv));
 
+	/* Make sure our arguments contain only valid UTF-8 characters. */
+	for (int i = 0; i < argc; i++) ValidateString(argv[i]);
+
 	openttd_main(argc, argv);
 	free(cmdline);
 	return 0;