diff --git a/libraries/AP_FlashStorage/examples/FlashTest/FlashTest.cpp b/libraries/AP_FlashStorage/examples/FlashTest/FlashTest.cpp
index 2240aebbe8..dd7a1b0c0d 100644
--- a/libraries/AP_FlashStorage/examples/FlashTest/FlashTest.cpp
+++ b/libraries/AP_FlashStorage/examples/FlashTest/FlashTest.cpp
@@ -128,7 +128,7 @@ void FlashTest::setup(void)
 
         if (erase_ok) {
             if (memcmp(mem_buffer, mem_mirror, sizeof(mem_buffer)) != 0) {
-                AP_HAL::panic("FATAL: data mis-match at i=%u", i);
+                AP_HAL::panic("FATAL: data mis-match at i=%u", (unsigned)i);
             }
         }
     }