diff --git a/src/rct2.c b/src/rct2.c
index 6feea21df6..15b3715392 100644
--- a/src/rct2.c
+++ b/src/rct2.c
@@ -230,7 +230,12 @@ void subsitute_path(char *dest, const char *path, const char *filename)
 // rct2: 0x00674B42
 void rct2_startup_checks()
 {
-	// check if game is already running
+	// Check if game is already running
+	if (check_mutex())
+	{
+		RCT2_ERROR("Game is already running");
+		RCT2_CALLPROC_X(0x006E3838, 0x343, 0xB2B, 0, 0, 0, 0, 0); // exit_with_error
+	}
 
 	RCT2_CALLPROC_EBPSAFE(0x00674C0B);
 }
@@ -303,6 +308,24 @@ void check_cmdline_arg()
 	}
 }
 
+// rct2: 0x00407DB0
+int check_mutex()
+{
+	const char * const mutex_name = "RollerCoaster Tycoon 2_GSKMUTEX"; // rct2 @ 0x009AAC3D + 0x009A8B50
+
+	HANDLE mutex = OpenMutex(MUTEX_ALL_ACCESS, FALSE, mutex_name);
+
+	if (mutex != NULL)
+	{
+		// Already running
+		CloseHandle(mutex);
+		return 1;
+	}
+
+	HANDLE status = CreateMutex(NULL, FALSE, mutex_name);
+	return 0;
+}
+
 void rct2_update_2()
 {
 	int tick, tick2;
diff --git a/src/rct2.h b/src/rct2.h
index cbb0dbdcfa..a03d1c7352 100644
--- a/src/rct2.h
+++ b/src/rct2.h
@@ -228,6 +228,7 @@ static const char * const file_paths[] =
 
 void rct2_endupdate();
 void subsitute_path(char *dest, const char *path, const char *filename);
+int check_mutex();
 const char *get_file_path(int pathId);
 void get_system_info();
 void get_system_time();