diff --git a/filters.cpp b/filters.cpp
index 6b09a02a..78fd6351 100644
--- a/filters.cpp
+++ b/filters.cpp
@@ -780,7 +780,8 @@ size_t HashFilter::Put2(const byte *inString, size_t length, int messageEnd, boo
 	FILTER_BEGIN;
 	if (m_putMessage)
 		FILTER_OUTPUT3(1, 0, inString, length, 0, m_messagePutChannel);
-	m_hashModule.Update(inString, length);
+	if (inString && length)
+		m_hashModule.Update(inString, length);
 	if (messageEnd)
 	{
 		{