diff --git a/libs/utils/Debug.cpp b/libs/utils/Debug.cpp
index f7988ec..e8ac983 100644
--- a/libs/utils/Debug.cpp
+++ b/libs/utils/Debug.cpp
@@ -199,7 +199,7 @@
     if ((int32_t)length < 0) {
         if (singleLineBytesCutoff < 0) func(cookie, "\n");
         char buf[64];
-        sprintf(buf, "(bad length: %d)", length);
+        sprintf(buf, "(bad length: %zu)", length);
         func(cookie, buf);
         return;
     }