diff --git a/stm-firmware/hw-version-detect.c b/stm-firmware/hw-version-detect.c
index d428d12..7dee01e 100644
--- a/stm-firmware/hw-version-detect.c
+++ b/stm-firmware/hw-version-detect.c
@@ -34,7 +34,8 @@
 enum hw_revision get_pcb_hardware_version(void)
 {
 	uint8_t current_pin;
-	uint16_t port_bitmask = 0U;
+	uint16_t port_bitmask = 0U; /* Use uint16_t because a port can have 16 IOs max. */
+	const uint16_t highest_bit_mask = (1 << (HW_REV_DETECT_PIN_HIGH - HW_REV_DETECT_PIN_LOW));
 	static enum hw_revision revision = HW_REV_NOT_DETECTED;
 
 	/* If the revision has been previously detected,
@@ -57,7 +58,7 @@ enum hw_revision get_pcb_hardware_version(void)
 	 */
 	for (current_pin = HW_REV_DETECT_PIN_LOW; current_pin <= HW_REV_DETECT_PIN_HIGH; current_pin++) {
 		port_bitmask >>= 1;
-		port_bitmask |= (HW_REV_DETECT_GPIO->IDR & (1 << current_pin)) ? 0x0 : 0x80;
+		port_bitmask |= (HW_REV_DETECT_GPIO->IDR & (1 << current_pin)) ? 0x0 : highest_bit_mask;
 	}
 
 	/* Resolve the read in bitmask to a hardware version */