diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index 266aedfe0..9b3ee4cf3 100644
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -5605,13 +5605,13 @@ bool RTLIL::SigSpec::is_chunk() const
 	return ++it == cs.end();
 }
 
-bool RTLIL::SigSpec::is_mostly_const() const
+bool RTLIL::SigSpec::is_mostly_const(double const_ratio_threshold) const
 {
 	int constbits = 0;
 	for (auto &chunk : chunks())
 		if (chunk.width > 0 && chunk.wire == NULL)
 			constbits += chunk.width;
-	return (constbits > size()/2);
+	return (constbits > size() * const_ratio_threshold);
 }
 
 bool RTLIL::SigSpec::known_driver() const
diff --git a/kernel/rtlil.h b/kernel/rtlil.h
index 9dfe0c570..7044e609a 100644
--- a/kernel/rtlil.h
+++ b/kernel/rtlil.h
@@ -1684,7 +1684,9 @@ public:
 
 	bool known_driver() const;
 
-	bool is_mostly_const() const;
+	// const_ratio_threshold is expected in [0.0, 1.0]
+	// boundary is exclusive, returns true only if const bit ratio > const_ratio_threshold
+	bool is_mostly_const(double const_ratio_threshold = 0.5) const;
 	bool is_fully_const() const;
 	bool is_fully_zero() const;
 	bool is_fully_ones() const;