diff --git a/Makefile b/Makefile
index 00aa30349..53b7a0326 100644
--- a/Makefile
+++ b/Makefile
@@ -70,6 +70,7 @@ $(B_DIR)/lib/ultra/libc/llcvt.o: MIPSISET := -mips3 -o32
 
 $(B_DIR)/lib/ultra/io/dpctr.o: OPT_LVL := -O1
 $(B_DIR)/lib/ultra/io/pigetcmdq.o: OPT_LVL := -O1
+$(B_DIR)/lib/ultra/io/si.o: OPT_LVL := -O1
 $(B_DIR)/lib/ultra/io/sp.o: OPT_LVL := -O1
 $(B_DIR)/lib/ultra/io/spsetpc.o: OPT_LVL := -O1
 $(B_DIR)/lib/ultra/io/sptaskyielded.o: OPT_LVL := -O1
diff --git a/src/lib/ultra/io/si.c b/src/lib/ultra/io/si.c
index 135d204d5..117af47f6 100644
--- a/src/lib/ultra/io/si.c
+++ b/src/lib/ultra/io/si.c
@@ -1,19 +1,12 @@
 #include <libultra_internal.h>
 
-GLOBAL_ASM(
-glabel __osSiDeviceBusy
-/*    51c60:	3c0ea480 */ 	lui	$t6,0xa480
-/*    51c64:	8dc40018 */ 	lw	$a0,0x18($t6)
-/*    51c68:	27bdfff8 */ 	addiu	$sp,$sp,-8
-/*    51c6c:	308f0003 */ 	andi	$t7,$a0,0x3
-/*    51c70:	11e00003 */ 	beqz	$t7,.L00051c80
-/*    51c74:	00000000 */ 	nop
-/*    51c78:	10000002 */ 	b	.L00051c84
-/*    51c7c:	24020001 */ 	addiu	$v0,$zero,0x1
-.L00051c80:
-/*    51c80:	00001025 */ 	or	$v0,$zero,$zero
-.L00051c84:
-/*    51c84:	03e00008 */ 	jr	$ra
-/*    51c88:	27bd0008 */ 	addiu	$sp,$sp,0x8
-/*    51c8c:	00000000 */ 	nop
-);
+int __osSiDeviceBusy()
+{
+	register u32 stat = IO_READ(SI_STATUS_REG);
+
+	if (stat & (SI_STATUS_DMA_BUSY | SI_STATUS_RD_BUSY)) {
+		return 1;
+	}
+
+	return 0;
+}