Getting closer.
diff --git a/src/core/linux/SDL_threadprio.c b/src/core/linux/SDL_threadprio.c
index 30a3748..edfe7d1 100644
--- a/src/core/linux/SDL_threadprio.c
+++ b/src/core/linux/SDL_threadprio.c
@@ -24,6 +24,7 @@
#include "SDL_error.h"
#include "SDL_stdinc.h"
+#include "SDL_thread.h"
#if !SDL_THREADS_DISABLED
#include <sys/time.h>