diff --git a/src/WSEvents.cpp b/src/WSEvents.cpp
index 159e5334..6dc62c8c 100644
--- a/src/WSEvents.cpp
+++ b/src/WSEvents.cpp
@@ -51,8 +51,7 @@ const char* nsToTimestamp(uint64_t ns) {
 	uint64_t msPart = ms % 1000;
 
 	char* ts = (char*)bmalloc(64);
-	sprintf(ts, "%02d:%02d:%02d.%03d",
-		hoursPart, minutesPart, secsPart, msPart);
+	sprintf(ts, "%02lu:%02lu:%02lu.%03lu", hoursPart, minutesPart, secsPart, msPart);
 
 	return ts;
 }