diff --git a/src/prolog/machine/machine_state_impl.rs b/src/prolog/machine/machine_state_impl.rs
index 82c0c4f2..998f3252 100644
--- a/src/prolog/machine/machine_state_impl.rs
+++ b/src/prolog/machine/machine_state_impl.rs
@@ -2201,6 +2201,9 @@ impl MachineState {
                     if ar1 != ar2 || n1 != n2 {
                         return true;
                     },
+                (HeapCellValue::Addr(Addr::PStrLocation(..)),
+                 HeapCellValue::Addr(Addr::PStrLocation(..))) =>
+                    continue,
                 (HeapCellValue::Addr(Addr::Lis(_)), HeapCellValue::Addr(Addr::Lis(_))) =>
                     continue,
                 (HeapCellValue::Addr(Addr::Con(Constant::EmptyList)),