diff --git a/src/analyzer/protocol/tcp/TCP_Endpoint.h b/src/analyzer/protocol/tcp/TCP_Endpoint.h
index 993c4b826b..df8acffdff 100644
--- a/src/analyzer/protocol/tcp/TCP_Endpoint.h
+++ b/src/analyzer/protocol/tcp/TCP_Endpoint.h
@@ -203,6 +203,7 @@ public:
 #define HIST_CORRUPT_PKT 0x80
 #define HIST_RXMIT 0x100
 #define HIST_WIN0 0x200
+    // #define HIST_UNKNOWN_PKT 0x400  (do not use - used in Session.h)
     bool CheckHistory(uint32_t mask, char code);
     void AddHistory(char code);
 
diff --git a/src/packet_analysis/protocol/udp/UDP.cc b/src/packet_analysis/protocol/udp/UDP.cc
index ae609e1dd3..5796d0969e 100644
--- a/src/packet_analysis/protocol/udp/UDP.cc
+++ b/src/packet_analysis/protocol/udp/UDP.cc
@@ -18,6 +18,7 @@ constexpr uint32_t HIST_ORIG_DATA_PKT = 0x1;
 constexpr uint32_t HIST_RESP_DATA_PKT = 0x2;
 constexpr uint32_t HIST_ORIG_CORRUPT_PKT = 0x4;
 constexpr uint32_t HIST_RESP_CORRUPT_PKT = 0x8;
+// constexpr uint32_t HIST_UNKNOWN_PKT = 0x400;  (do not use - used in Session.h)
 
 UDPAnalyzer::UDPAnalyzer() : IPBasedAnalyzer("UDP", TRANSPORT_UDP, UDP_PORT_MASK, false) {}
 
diff --git a/src/session/Session.h b/src/session/Session.h
index 589c39af71..467dd9c9af 100644
--- a/src/session/Session.h
+++ b/src/session/Session.h
@@ -24,7 +24,9 @@ class Analyzer;
 namespace session {
 namespace detail {
 class Timer;
-}
+
+constexpr uint32_t HIST_UNKNOWN_PKT = 0x400; // Initially for exceeded_tunnel_max_depth.
+} // namespace detail
 
 class Session;
 using timer_func = void (Session::*)(double t);