diff --git a/passes/pmgen/peepopt_shiftadd.pmg b/passes/pmgen/peepopt_shiftadd.pmg
index 875559790..161effe43 100644
--- a/passes/pmgen/peepopt_shiftadd.pmg
+++ b/passes/pmgen/peepopt_shiftadd.pmg
@@ -63,7 +63,8 @@ match add
 
 	define <bool> constport_signed param(add, !varport_A ? \A_SIGNED : \B_SIGNED).as_bool()
 	define <bool> varport_signed param(add, varport_A ? \A_SIGNED : \B_SIGNED).as_bool();
-	define <bool> offset_negative ((port(add, constport).bits().back() == State::S1) ^ (is_sub && varport_A))
+	define <bool> const_negative (constport_signed && (port(add, constport).bits().back() == State::S1))
+	define <bool> offset_negative ((is_sub && varport_A) ^ const_negative)
 
 	// checking some value boundaries as well:
 	// data[...-c +:W1] is fine for any signed var (pad at LSB, all data still accessible)