diff --git a/boot/zephyr/CMakeLists.txt b/boot/zephyr/CMakeLists.txt
index 9156ad23d..f6c4b7eea 100644
--- a/boot/zephyr/CMakeLists.txt
+++ b/boot/zephyr/CMakeLists.txt
@@ -433,8 +433,12 @@ if(SYSBUILD)
     if(NOT DEFINED write_size)
       message(WARNING "Unable to determine write size of slot0 or slot1 partition, setting to 8 (this is probably wrong)")
       set(write_size 8)
-    elseif(write_size LESS 8)
-      set(write_size 8)
+    endif()
+
+    if(${write_size} LESS 8)
+      set(max_align_size 8)
+    else()
+      set(max_align_size ${write_size})
     endif()
 
     set(key_size 0)
@@ -473,7 +477,7 @@ if(SYSBUILD)
         set(key_size "${boot_enc_key_size}")
       endif()
 
-      align_up(${key_size} ${write_size} key_size)
+      align_up(${key_size} ${max_align_size} key_size)
       math(EXPR key_size "${key_size} * 2")
     endif()
 
@@ -482,7 +486,7 @@ if(SYSBUILD)
     if(CONFIG_SINGLE_APPLICATION_SLOT OR CONFIG_BOOT_FIRMWARE_LOADER)
       set(boot_swap_data_size 0)
     else()
-      math(EXPR boot_swap_data_size "${write_size} * 4")
+      math(EXPR boot_swap_data_size "${max_align_size} * 4")
     endif()
 
     if(CONFIG_BOOT_SWAP_USING_SCRATCH OR CONFIG_BOOT_SWAP_USING_MOVE)