--- 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_ */
--- a/src-plugins/nhdp/nhdp/nhdp_internal.h
+++ b/src-plugins/nhdp/nhdp/nhdp_internal.h
@@ -49,8 +49,8 @@
 #include "core/oonf_logging.h"
 
 /* headers only for use inside the NHDP subsystem */
-enum oonf_log_source LOG_NHDP;
-enum oonf_log_source LOG_NHDP_R;
-enum oonf_log_source LOG_NHDP_W;
+extern enum oonf_log_source LOG_NHDP;
+extern enum oonf_log_source LOG_NHDP_R;
+extern enum oonf_log_source LOG_NHDP_W;
 
 #endif /* NHDP_INTERNAL_H_ */
--- a/src-plugins/olsrv2/olsrv2/olsrv2_internal.h
+++ b/src-plugins/olsrv2/olsrv2/olsrv2_internal.h
@@ -50,9 +50,9 @@
 #include "core/oonf_logging.h"
 
 /* headers only for use inside the OLSRv2 subsystem */
-EXPORT enum oonf_log_source LOG_OLSRV2;
-EXPORT enum oonf_log_source LOG_OLSRV2_R;
-EXPORT enum oonf_log_source LOG_OLSRV2_ROUTING;
-EXPORT enum oonf_log_source LOG_OLSRV2_W;
+EXPORT extern enum oonf_log_source LOG_OLSRV2;
+EXPORT extern enum oonf_log_source LOG_OLSRV2_R;
+EXPORT extern enum oonf_log_source LOG_OLSRV2_ROUTING;
+EXPORT extern enum oonf_log_source LOG_OLSRV2_W;
 
 #endif /* OLSRV2_INTERNAL_H_ */