diff --git a/core/assert.c b/core/assert.c
index 35c9d5359e..873634467d 100644
--- a/core/assert.c
+++ b/core/assert.c
@@ -20,7 +20,7 @@
 #ifdef DEBUG_ASSERT_VERBOSE
 NORETURN void _assert_failure(const char *file, unsigned line)
 {
-    printf("%s:%d => ", file, line); \
+    printf("%s:%u => ", file, line); \
     core_panic(PANIC_ASSERT_FAIL, assert_crash_message); \
 }
 #else