diff --git a/Disk.cpp b/Disk.cpp
index 920edab..2872029 100644
--- a/Disk.cpp
+++ b/Disk.cpp
@@ -236,7 +236,7 @@
     }
     }
 
-    notifyEvent(ResponseCode::DiskSizeChanged, StringPrintf("%" PRId64, mSize));
+    notifyEvent(ResponseCode::DiskSizeChanged, StringPrintf("%" PRIu64, mSize));
     notifyEvent(ResponseCode::DiskLabelChanged, mLabel);
     notifyEvent(ResponseCode::DiskSysPathChanged, mSysPath);
     return OK;