diff --git a/src/BOPTools/BOPTools_Set.cxx b/src/BOPTools/BOPTools_Set.cxx
index 8cd2576fe6..f5e0a6e01b 100644
--- a/src/BOPTools/BOPTools_Set.cxx
+++ b/src/BOPTools/BOPTools_Set.cxx
@@ -157,6 +157,7 @@ void BOPTools_Set::Add(const TopoDS_Shape& theS,
                        const TopAbs_ShapeEnum theType)
 {
   Standard_Integer aId, aIdN;
+  TopAbs_Orientation aOr;
   TopExp_Explorer aExp;
   //
   myShape=theS;
@@ -173,7 +174,22 @@ void BOPTools_Set::Add(const TopoDS_Shape& theS,
         continue;
       }
     }
-    myShapes.Append(aSx);
+    //
+    aOr=aSx.Orientation();
+    if (aOr==TopAbs_INTERNAL) {
+      TopoDS_Shape aSy;
+      //
+      aSy=aSx;
+      //
+      aSy.Orientation(TopAbs_FORWARD);
+      myShapes.Append(aSy);
+      //
+      aSy.Orientation(TopAbs_REVERSED);
+      myShapes.Append(aSy);
+    }
+    else {
+      myShapes.Append(aSx);
+    }
   }
   //
   myNbShapes=myShapes.Extent();
diff --git a/tests/bugs/modalg_5/bug25721 b/tests/bugs/modalg_5/bug25721
new file mode 100644
index 0000000000..3c525a6258
--- /dev/null
+++ b/tests/bugs/modalg_5/bug25721
@@ -0,0 +1,33 @@
+puts "========="
+puts "OCC25721"
+puts "========="
+puts ""
+###############################################
+# Wrong result obtained by Common operator.
+###############################################
+
+restore [locate_data_file bug25721_qf1] qf
+explode qf
+copy qf_1 b1
+copy qf_2 b2
+
+bclearobjects
+bcleartools
+baddobjects b1
+baddtools b2
+
+bfillds
+bbop result 0
+
+set square 181.203
+set nb_v_good 2
+set nb_e_good 3
+set nb_w_good 3
+set nb_f_good 1
+set nb_sh_good 1
+set nb_sol_good 0
+set nb_compsol_good 0
+set nb_compound_good 1
+set nb_shape_good 11
+
+set 2dviewer 1