--- a/src-plugins/generic/dlep/radio/dlep_radio_internal.h
+++ b/src-plugins/generic/dlep/radio/dlep_radio_internal.h
@@ -49,6 +49,6 @@
 #include "core/oonf_logging.h"
 
 /* headers only for use inside the DLEP_RADIO subsystem */
-enum oonf_log_source LOG_DLEP_RADIO;
+extern enum oonf_log_source LOG_DLEP_RADIO;
 
 #endif /* DLEP_RADIO_INTERNAL_H_ */
--- a/src-plugins/generic/dlep/router/dlep_router_internal.h
+++ b/src-plugins/generic/dlep/router/dlep_router_internal.h
@@ -49,6 +49,6 @@
 #include "core/oonf_logging.h"
 
 /* headers only for use inside the DLEP_ROUTER subsystem */
-enum oonf_log_source LOG_DLEP_ROUTER;
+extern enum oonf_log_source LOG_DLEP_ROUTER;
 
 #endif /* DLEP_ROUTER_INTERNAL_H_ */
--- a/src-plugins/generic/nl80211_listener/nl80211_internal.h
+++ b/src-plugins/generic/nl80211_listener/nl80211_internal.h
@@ -49,6 +49,6 @@
 #include "core/oonf_logging.h"
 
 /* headers only for use inside the NL80211 subsystem */
-enum oonf_log_source LOG_NL80211;
+extern enum oonf_log_source LOG_NL80211;
 
 #endif /* NL80211_INTERNAL_H_ */