diff --git a/boot/zephyr/boards/nrf52840_pca10059.conf b/boot/zephyr/boards/nrf52840_pca10059.conf
index 8c59700..ba333d9 100644
--- a/boot/zephyr/boards/nrf52840_pca10059.conf
+++ b/boot/zephyr/boards/nrf52840_pca10059.conf
@@ -3,6 +3,10 @@
 # Disable logging.
 CONFIG_LOG=n
 
+# The build won't fit on the partition allocated for it without size
+# optimizations.
+CONFIG_SIZE_OPTIMIZATIONS=y
+
 # Serial
 CONFIG_SERIAL=y
 CONFIG_UART_NRFX=y