diff --git a/sysmoOCTSIM/atmel_start.h b/sysmoOCTSIM/atmel_start.h
index 4892cbd..fb1e18f 100644
--- a/sysmoOCTSIM/atmel_start.h
+++ b/sysmoOCTSIM/atmel_start.h
@@ -12,7 +12,7 @@
 #include "stdio_start.h"
 
 /** flag set when the memory to memory DMA is complete */
-volatile bool dma_m2m_complete_flag;
+extern volatile bool dma_m2m_complete_flag;
 
 /**
  * Initializes MCU, drivers and middleware in the project