diff --git a/df_datalink_sp/src/system_monitor.c b/df_datalink_sp/src/system_monitor.c
index feb9a7e..b7a1046 100644
--- a/df_datalink_sp/src/system_monitor.c
+++ b/df_datalink_sp/src/system_monitor.c
@@ -46,7 +46,8 @@ uint8_t GetReadable(PINGPONG ctrllor);
 
 inline uint8_t GetWritable(PINGPONG ctrllor)
 {
-	ASSERT(ctrllor.wBusy != BUFF_NONE);
+	// Allow only one write.
+	ASSERT(ctrllor.wBusy == BUFF_NONE);
 	if (ctrllor.rBusy == BUFF_NONE)
 		return ((ctrllor.latest == BUFF_B) ? BUFF_A : BUFF_B);
 	else