--- a/plugins/nd/src/backend.h
+++ b/plugins/nd/src/backend.h
@@ -37,7 +37,7 @@
     _EVENTD_ND_BACKENDS_SIZE
 } EventdNdBackends;
 
-const gchar *eventd_nd_backends_names[_EVENTD_ND_BACKENDS_SIZE];
+extern const gchar *eventd_nd_backends_names[_EVENTD_ND_BACKENDS_SIZE];
 
 typedef struct {
     EventdNdContext *context;