diff --git a/libraries/AP_HAL_ChibiOS/Util.cpp b/libraries/AP_HAL_ChibiOS/Util.cpp
index dfe42a39bd..e839b41463 100644
--- a/libraries/AP_HAL_ChibiOS/Util.cpp
+++ b/libraries/AP_HAL_ChibiOS/Util.cpp
@@ -178,6 +178,9 @@ bool Util::flash_bootloader()
         return false;
     }
 
+    // make sure size is multiple of 32
+    fw_size = (fw_size + 31U) & ~31U;
+
     const uint32_t addr = hal.flash->getpageaddr(0);
     if (!memcmp(fw, (const void*)addr, fw_size)) {
         hal.console->printf("Bootloader up-to-date\n");