diff --git a/src/ccallsign.cpp b/src/ccallsign.cpp
index 77f5a58..adaa78d 100644
--- a/src/ccallsign.cpp
+++ b/src/ccallsign.cpp
@@ -338,7 +338,7 @@ CCallsign::operator const char *() const
 	// module
 	if ( HasModule() )
 	{
-		m_sz[sizeof(m_Callsign)] = m_Module;
+		m_sz[sizeof(m_Callsign) - 1] = m_Module;
 	}
 	// suffix
 	if ( HasSuffix() )