diff --git a/include/grub/ns8250.h b/include/grub/ns8250.h
index 2dcd07f14..7947ba9c9 100644
--- a/include/grub/ns8250.h
+++ b/include/grub/ns8250.h
@@ -70,9 +70,11 @@
 /* Turn on DTR, RTS, and OUT2.  */
 #define UART_ENABLE_OUT2	0x08
 
+#ifndef ASM_FILE
 #include <grub/cpu/io.h>
 
 grub_port_t
 grub_ns8250_hw_get_port (const unsigned int unit);
+#endif
 
 #endif /* ! GRUB_SERIAL_MACHINE_HEADER */