diff --git a/code/datums/wounds/bones.dm b/code/datums/wounds/bones.dm
index 93ca9c5b67..230fc6758f 100644
--- a/code/datums/wounds/bones.dm
+++ b/code/datums/wounds/bones.dm
@@ -390,7 +390,7 @@
 		if(victim.reagents && victim.reagents.has_reagent(/datum/reagent/determination))
 			painkiller_bonus += 5
 
-		if(prob(25 + (20 * severity - 2) - painkiller_bonus)) // 25%/45% chance to fail self-applying with severe and critical wounds, modded by painkillers
+		if(prob(25 + (20 * (severity - 2)) - painkiller_bonus)) // 25%/45% chance to fail self-applying with severe and critical wounds, modded by painkillers
 			victim.visible_message("<span class='danger'>[victim] fails to finish applying [I] to [victim.p_their()] [limb.name], passing out from the pain!</span>", "<span class='notice'>You black out from the pain of applying [I] to your [limb.name] before you can finish!</span>")
 			victim.AdjustUnconscious(5 SECONDS)
 			return