diff --git a/boot/arm-trusted-firmware/arm-trusted-firmware.mk b/boot/arm-trusted-firmware/arm-trusted-firmware.mk
index 172a930b5c..decfd4748f 100644
--- a/boot/arm-trusted-firmware/arm-trusted-firmware.mk
+++ b/boot/arm-trusted-firmware/arm-trusted-firmware.mk
@@ -162,6 +162,8 @@ endif
 
 ifeq ($(BR2_TARGET_ARM_TRUSTED_FIRMWARE_BL31),y)
 ARM_TRUSTED_FIRMWARE_MAKE_TARGETS += bl31
+# Avoid BL31 environment variable from polluting the build
+ARM_TRUSTED_FIRMWARE_MAKE_OPTS += BL31=
 endif
 
 ifeq ($(BR2_TARGET_ARM_TRUSTED_FIRMWARE_BL31_UBOOT),y)