diff --git a/code/modules/mob/living/carbon/human/human_defense.dm b/code/modules/mob/living/carbon/human/human_defense.dm
index a6fa8e23e6b..8396b90ee44 100644
--- a/code/modules/mob/living/carbon/human/human_defense.dm
+++ b/code/modules/mob/living/carbon/human/human_defense.dm
@@ -215,7 +215,7 @@ emp_act
 
 //End Here
 
-#define BLOCK_CHANCE_CALCULATION(hand_block_chance, armour_penetration_flat, armour_penetration_percentage, block_chance_modifier) clamp((hand_block_chance * ((100-armour_penetration_percentage) / 100)) - armour_penetration_flat + block_chance_modifier, 0, 100)
+#define BLOCK_CHANCE_CALCULATION(hand_block_chance, armour_penetration_flat, armour_penetration_percentage, block_chance_modifier) clamp((hand_block_chance * ((100-armour_penetration_percentage) / 100)) - max(armour_penetration_flat, 0) + block_chance_modifier, 0, 100)
 
 /mob/living/carbon/human/proc/check_shields(atom/AM, damage, attack_text = "the attack", attack_type = MELEE_ATTACK, armour_penetration_flat = 0, armour_penetration_percentage = 0)
 	var/block_chance_modifier = round(damage / -3)