diff --git a/passes/opt/opt_expr.cc b/passes/opt/opt_expr.cc
index 7afb380a2..9ccc230e8 100644
--- a/passes/opt/opt_expr.cc
+++ b/passes/opt/opt_expr.cc
@@ -383,7 +383,8 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 		if (detect_const_and || detect_const_or)
 		{
 			pool<SigBit> input_bits = assign_map(cell->getPort("\\A")).to_sigbit_pool();
-			bool found_zero = false, found_one = false, found_inv = false;
+			bool found_zero = false, found_one = false, found_undef = false, found_inv = false, many_conconst = false;
+			SigBit non_const_input = State::Sm;
 
 			if (cell->hasPort("\\B")) {
 				vector<SigBit> more_bits = assign_map(cell->getPort("\\B")).to_sigbit_vector();
@@ -391,12 +392,20 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 			}
 
 			for (auto bit : input_bits) {
-				if (bit == State::S0)
-					found_zero = true;
-				if (bit == State::S1)
-					found_one = true;
-				if (invert_map.count(bit) && input_bits.count(invert_map.at(bit)))
-					found_inv = true;
+				if (bit.wire) {
+					if (invert_map.count(bit) && input_bits.count(invert_map.at(bit)))
+						found_inv = true;
+					if (non_const_input != State::Sm)
+						many_conconst = true;
+					non_const_input = many_conconst ? State::Sm : bit;
+				} else {
+					if (bit == State::S0)
+						found_zero = true;
+					else if (bit == State::S1)
+						found_one = true;
+					else
+						found_undef = true;
+				}
 			}
 
 			if (detect_const_and && (found_zero || found_inv)) {
@@ -410,6 +419,12 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
 				replace_cell(assign_map, module, cell, "const_or", "\\Y", RTLIL::State::S1);
 				goto next_cell;
 			}
+
+			if (non_const_input != State::Sm && !found_undef) {
+				cover("opt.opt_expr.and_or_buffer");
+				replace_cell(assign_map, module, cell, "and_or_buffer", "\\Y", non_const_input);
+				goto next_cell;
+			}
 		}
 
 		if (cell->type.in("$reduce_and", "$reduce_or", "$reduce_bool", "$reduce_xor", "$reduce_xnor", "$neg") &&