--- a/plc/plc.h
+++ b/plc/plc.h
@@ -498,7 +498,7 @@ struct __packed plcproperty
 	uint8_t DATA_BUFFER [128];
 }
 
-plcproperty;
+extern plcproperty;
 
 #ifndef __GNUC__
 #pragma pack (pop)