diff --git a/drivers/avr/ssd1306.c b/drivers/avr/ssd1306.c
index 205f749502b8..1a09a2bcb789 100644
--- a/drivers/avr/ssd1306.c
+++ b/drivers/avr/ssd1306.c
@@ -11,6 +11,8 @@
 #    include "sendchar.h"
 #    include "timer.h"
 
+struct CharacterMatrix display;
+
 // Set this to 1 to help diagnose early startup problems
 // when testing power-on with ble.  Turn it off otherwise,
 // as the latency of printing most of the debug info messes
diff --git a/drivers/avr/ssd1306.h b/drivers/avr/ssd1306.h
index 9669d1b7e77e..9131afcf6122 100644
--- a/drivers/avr/ssd1306.h
+++ b/drivers/avr/ssd1306.h
@@ -66,7 +66,7 @@ struct CharacterMatrix {
     bool     dirty;
 };
 
-struct CharacterMatrix display;
+extern struct CharacterMatrix display;
 
 bool iota_gfx_init(void);
 void iota_gfx_task(void);