add missing include.
diff --git a/src/dynapi/SDL_dynapi.c b/src/dynapi/SDL_dynapi.c
index 7574cf5..97bc218 100644
--- a/src/dynapi/SDL_dynapi.c
+++ b/src/dynapi/SDL_dynapi.c
@@ -27,6 +27,7 @@
#if defined(__OS2__)
#define INCL_DOS
#define INCL_DOSERRORS
+#include <os2.h>
#include <dos.h>
#endif