diff --git a/solanaceae/ngc_ft1/cca.hpp b/solanaceae/ngc_ft1/cca.hpp
index 4d8a9d2..8117bc5 100644
--- a/solanaceae/ngc_ft1/cca.hpp
+++ b/solanaceae/ngc_ft1/cca.hpp
@@ -70,5 +70,8 @@ struct CCAI {
 
 		// if discard, not resent, not inflight
 		virtual void onLoss(SeqIDType seq, bool discard) = 0;
+
+		// signal congestion externally (eg. send queue is full)
+		virtual void onCongestion(void) {};
 };
 
diff --git a/solanaceae/ngc_ft1/flow_only.hpp b/solanaceae/ngc_ft1/flow_only.hpp
index d0bdc79..9db0a2c 100644
--- a/solanaceae/ngc_ft1/flow_only.hpp
+++ b/solanaceae/ngc_ft1/flow_only.hpp
@@ -58,8 +58,6 @@ struct FlowOnly : public CCAI {
 
 		void updateWindow(void);
 
-		virtual void onCongestion(void) {};
-
 		// internal logic, calls the onCongestion() event
 		void updateCongestion(void);