diff --git a/src/os/os2/os2.cpp b/src/os/os2/os2.cpp
index 5d35eca451..0b2d8de6a5 100644
--- a/src/os/os2/os2.cpp
+++ b/src/os/os2/os2.cpp
@@ -223,3 +223,4 @@ void PerThreadSetupInit() { }
 bool IsMainThread() { return false; }
 bool IsNonMainThread() { return false; }
 bool IsGameThread() { return false; }
+bool IsNonGameThread() { return false; }
diff --git a/src/os/unix/unix.cpp b/src/os/unix/unix.cpp
index 2479c6fe8c..0f53fb1727 100644
--- a/src/os/unix/unix.cpp
+++ b/src/os/unix/unix.cpp
@@ -380,6 +380,15 @@ bool IsGameThread()
 {
 #if !defined(NO_THREADS)
 	return game_thread == pthread_self();
+#else
+	return true;
+#endif
+}
+
+bool IsNonGameThread()
+{
+#if !defined(NO_THREADS)
+	return game_thread != pthread_self();
 #else
 	return false;
 #endif
diff --git a/src/os/windows/win32.cpp b/src/os/windows/win32.cpp
index afef3313c7..70716e8f3b 100644
--- a/src/os/windows/win32.cpp
+++ b/src/os/windows/win32.cpp
@@ -757,6 +757,11 @@ bool IsGameThread()
 	return game_thread_id == GetCurrentThreadId();
 }
 
+bool IsNonGameThread()
+{
+	return game_thread_id != GetCurrentThreadId();
+}
+
 static std::map<DWORD, std::string> _thread_name_map;
 static std::mutex _thread_name_map_mutex;
 
diff --git a/src/saveload/saveload.cpp b/src/saveload/saveload.cpp
index e28f8b0b76..98bcd02a4c 100644
--- a/src/saveload/saveload.cpp
+++ b/src/saveload/saveload.cpp
@@ -386,7 +386,7 @@ void NORETURN SlError(StringID string, const char *extra_msg, bool already_mallo
 		str = already_malloced ? const_cast<char *>(extra_msg) : stredup(extra_msg);
 	}
 
-	if (IsNonMainThread() && !IsGameThread() && _sl.action != SLA_SAVE) {
+	if (IsNonMainThread() && IsNonGameThread() && _sl.action != SLA_SAVE) {
 		throw ThreadSlErrorException{ string, extra_msg };
 	}
 
diff --git a/src/thread.h b/src/thread.h
index 7860bfaf78..66581b7573 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -76,6 +76,11 @@ bool IsNonMainThread();
  */
 bool IsGameThread();
 
+/**
+ * @return true if the current thread is definitely a "non-game" thread. If in doubt returns false.
+ */
+bool IsNonGameThread();
+
 
 /**
  * Start a new thread.
diff --git a/src/video/null_v.cpp b/src/video/null_v.cpp
index e5fc79faee..78b660258f 100644
--- a/src/video/null_v.cpp
+++ b/src/video/null_v.cpp
@@ -11,6 +11,7 @@
 #include "../gfx_func.h"
 #include "../blitter/factory.hpp"
 #include "../window_func.h"
+#include "../thread.h"
 #include "null_v.h"
 
 #include "../safeguards.h"
@@ -48,6 +49,7 @@ void VideoDriver_Null::MakeDirty(int left, int top, int width, int height) {}
 
 void VideoDriver_Null::MainLoop()
 {
+	SetSelfAsGameThread();
 	if (this->until_exit) {
 		while (!_exit_game) {
 			::GameLoop();