diff --git a/boot/zephyr/prj.conf b/boot/zephyr/prj.conf
index 510fe905..27efab57 100644
--- a/boot/zephyr/prj.conf
+++ b/boot/zephyr/prj.conf
@@ -14,7 +14,8 @@ CONFIG_HEAP_MEM_POOL_SIZE=16384
 CONFIG_FLASH=y
 CONFIG_MPU_ALLOW_FLASH_WRITE=y
 
-### Disable Bluetooth by default
-# CONFIG_BT is not set
-
 CONFIG_MULTITHREADING=n
+
+### Zephyr keeps turning on major subsystems by default that we don't want.
+# CONFIG_BT is not set
+# CONFIG_I2C is not set