diff --git a/boot/zephyr/flash_map_extended.c b/boot/zephyr/flash_map_extended.c
index 7133c99..4f6749b 100644
--- a/boot/zephyr/flash_map_extended.c
+++ b/boot/zephyr/flash_map_extended.c
@@ -67,4 +67,10 @@
     sector->fs_size = page.size;
 
     return rc;
-}
\ No newline at end of file
+}
+
+uint8_t flash_area_erased_val(const struct flash_area *fap)
+{
+    (void)fap;
+    return 0xff;
+}
diff --git a/boot/zephyr/include/flash_map_backend/flash_map_backend.h b/boot/zephyr/include/flash_map_backend/flash_map_backend.h
index d09aa59..ae347cf 100644
--- a/boot/zephyr/include/flash_map_backend/flash_map_backend.h
+++ b/boot/zephyr/include/flash_map_backend/flash_map_backend.h
@@ -58,6 +58,12 @@
  */
 int flash_area_sector_from_off(off_t off, struct flash_sector *sector);
 
+/*
+ * Returns the value expected to be read when accesing any erased
+ * flash byte.
+ */
+uint8_t flash_area_erased_val(const struct flash_area *fap);
+
 #ifdef __cplusplus
 }
 #endif