diff --git a/Makefile b/Makefile
index 5f01da16c..11848c626 100644
--- a/Makefile
+++ b/Makefile
@@ -75,6 +75,7 @@ $(B_DIR)/lib/ultra/io/vigetnextframebuf.o: OPT_LVL := -O1
 $(B_DIR)/lib/ultra/io/visetevent.o: OPT_LVL := -O1
 $(B_DIR)/lib/ultra/os/destroythread.o: OPT_LVL := -O1
 $(B_DIR)/lib/ultra/os/resetglobalintmask.o: OPT_LVL := -O1
+$(B_DIR)/lib/ultra/os/setthreadpri.o: OPT_LVL := -O1
 $(B_DIR)/lib/ultra/os/stopthread.o: OPT_LVL := -O1
 $(B_DIR)/lib/ultra/os/thread.o: OPT_LVL := -O1
 $(B_DIR)/lib/ultra/os/yieldthread.o: OPT_LVL := -O1
diff --git a/src/lib/ultra/os/setthreadpri.c b/src/lib/ultra/os/setthreadpri.c
index 91283a5e9..6b2fd3210 100644
--- a/src/lib/ultra/os/setthreadpri.c
+++ b/src/lib/ultra/os/setthreadpri.c
@@ -1,64 +1,27 @@
 #include <libultra_internal.h>
+#include "game/data/data_000000.h"
 
-GLOBAL_ASM(
-glabel osSetThreadPri
-/*    48430:	27bdffd8 */ 	addiu	$sp,$sp,-40
-/*    48434:	afbf001c */ 	sw	$ra,0x1c($sp)
-/*    48438:	afa40028 */ 	sw	$a0,0x28($sp)
-/*    4843c:	afa5002c */ 	sw	$a1,0x2c($sp)
-/*    48440:	0c01256c */ 	jal	__osDisableInt
-/*    48444:	afb00018 */ 	sw	$s0,0x18($sp)
-/*    48448:	8fae0028 */ 	lw	$t6,0x28($sp)
-/*    4844c:	00408025 */ 	or	$s0,$v0,$zero
-/*    48450:	15c00004 */ 	bnez	$t6,.L00048464
-/*    48454:	00000000 */ 	nop
-/*    48458:	3c0f8006 */ 	lui	$t7,%hi(__osRunningThread)
-/*    4845c:	8def0940 */ 	lw	$t7,%lo(__osRunningThread)($t7)
-/*    48460:	afaf0028 */ 	sw	$t7,0x28($sp)
-.L00048464:
-/*    48464:	8fb80028 */ 	lw	$t8,0x28($sp)
-/*    48468:	8fa8002c */ 	lw	$t0,0x2c($sp)
-/*    4846c:	8f190004 */ 	lw	$t9,0x4($t8)
-/*    48470:	13280020 */ 	beq	$t9,$t0,.L000484f4
-/*    48474:	00000000 */ 	nop
-/*    48478:	af080004 */ 	sw	$t0,0x4($t8)
-/*    4847c:	3c0a8006 */ 	lui	$t2,%hi(__osRunningThread)
-/*    48480:	8d4a0940 */ 	lw	$t2,%lo(__osRunningThread)($t2)
-/*    48484:	8fa90028 */ 	lw	$t1,0x28($sp)
-/*    48488:	112a000c */ 	beq	$t1,$t2,.L000484bc
-/*    4848c:	00000000 */ 	nop
-/*    48490:	952b0010 */ 	lhu	$t3,0x10($t1)
-/*    48494:	24010001 */ 	addiu	$at,$zero,0x1
-/*    48498:	11610008 */ 	beq	$t3,$at,.L000484bc
-/*    4849c:	00000000 */ 	nop
-/*    484a0:	8d240008 */ 	lw	$a0,0x8($t1)
-/*    484a4:	0c012884 */ 	jal	__osDequeueThread
-/*    484a8:	01202825 */ 	or	$a1,$t1,$zero
-/*    484ac:	8fac0028 */ 	lw	$t4,0x28($sp)
-/*    484b0:	8d840008 */ 	lw	$a0,0x8($t4)
-/*    484b4:	0c000f2e */ 	jal	__osEnqueueThread
-/*    484b8:	01802825 */ 	or	$a1,$t4,$zero
-.L000484bc:
-/*    484bc:	3c0d8006 */ 	lui	$t5,%hi(__osRunningThread)
-/*    484c0:	3c0f8006 */ 	lui	$t7,%hi(__osRunQueue)
-/*    484c4:	8def0938 */ 	lw	$t7,%lo(__osRunQueue)($t7)
-/*    484c8:	8dad0940 */ 	lw	$t5,%lo(__osRunningThread)($t5)
-/*    484cc:	8df90004 */ 	lw	$t9,0x4($t7)
-/*    484d0:	8dae0004 */ 	lw	$t6,0x4($t5)
-/*    484d4:	01d9082a */ 	slt	$at,$t6,$t9
-/*    484d8:	10200006 */ 	beqz	$at,.L000484f4
-/*    484dc:	00000000 */ 	nop
-/*    484e0:	24080002 */ 	addiu	$t0,$zero,0x2
-/*    484e4:	3c048006 */ 	lui	$a0,%hi(__osRunQueue)
-/*    484e8:	a5a80010 */ 	sh	$t0,0x10($t5)
-/*    484ec:	0c000ee8 */ 	jal	__osEnqueueAndYield
-/*    484f0:	24840938 */ 	addiu	$a0,$a0,%lo(__osRunQueue)
-.L000484f4:
-/*    484f4:	0c012588 */ 	jal	__osRestoreInt
-/*    484f8:	02002025 */ 	or	$a0,$s0,$zero
-/*    484fc:	8fbf001c */ 	lw	$ra,0x1c($sp)
-/*    48500:	8fb00018 */ 	lw	$s0,0x18($sp)
-/*    48504:	27bd0028 */ 	addiu	$sp,$sp,0x28
-/*    48508:	03e00008 */ 	jr	$ra
-/*    4850c:	00000000 */ 	nop
-);
+void osSetThreadPri(OSThread *t, OSPri pri)
+{
+	register u32 saveMask = __osDisableInt();
+
+	if (t == NULL) {
+		t = __osRunningThread;
+	}
+
+	if (t->priority != pri) {
+		t->priority = pri;
+
+		if (t != __osRunningThread && t->state != OS_STATE_STOPPED) {
+			__osDequeueThread(t->queue, t);
+			__osEnqueueThread(t->queue, t);
+		}
+
+		if (__osRunningThread->priority < __osRunQueue->priority) {
+			__osRunningThread->state = OS_STATE_RUNNABLE;
+			__osEnqueueAndYield(&__osRunQueue);
+		}
+	}
+
+	__osRestoreInt(saveMask);
+}