diff --git a/src/script/script.h b/src/script/script.h
index c09899aabd..d15b9c7550 100644
--- a/src/script/script.h
+++ b/src/script/script.h
@@ -23,6 +23,10 @@ static const unsigned int MAX_SCRIPT_ELEMENT_SIZE = 520; // bytes
 // otherwise as UNIX timestamp.
 static const unsigned int LOCKTIME_THRESHOLD = 500000000; // Tue Nov  5 00:53:20 1985 UTC
 
+// Threshold for inverted CTxIn::nSequence: below this value it is interpreted
+// as a relative lock-time, otherwise ignored.
+static const uint32_t SEQUENCE_THRESHOLD = (1 << 31);
+
 template <typename T>
 std::vector<unsigned char> ToByteVector(const T& in)
 {