diff --git a/src/subtitle_format_ebu3264.cpp b/src/subtitle_format_ebu3264.cpp
index 4c47fa54f..37f6d139d 100644
--- a/src/subtitle_format_ebu3264.cpp
+++ b/src/subtitle_format_ebu3264.cpp
@@ -531,7 +531,7 @@ namespace
 		char buf[16];
 		va_list ap;
 		va_start(ap, format);
-		vsnprintf(buf, fieldlen, format, ap);
+		vsnprintf(buf, sizeof(buf), format, ap);
 		va_end(ap);
 		memcpy(field, buf, fieldlen);
 	}