--- a/plugins/mod_http_file_share.lua	Wed Jan 27 00:29:12 2021 +0100
+++ b/plugins/mod_http_file_share.lua	Wed Jan 27 00:36:49 2021 +0100
@@ -48,6 +48,7 @@
 	filetype = { type = "modify"; condition = "not-acceptable"; text = "File type not allowed" };
 	filesize = { type = "modify"; condition = "not-acceptable"; text = "File too large";
 		extra = {tag = st.stanza("file-too-large", {xmlns = namespace}):tag("max-file-size"):text(tostring(file_size_limit)) };
+	filesizefmt = { type = "modify"; condition = "bad-request"; text = "File size must be positive integer"; }
 	};
 });
 
@@ -62,6 +63,9 @@
 		return false, upload_errors.new("filename");
 	end
 
+	if not filesize or filesize < 0 or filesize % 1 ~= 0 then
+		return false, upload_errors.new("filesizefmt");
+	end
 	if filesize > file_size_limit then
 		return false, upload_errors.new("filesize");
 	end