diff --git a/src/BOPTools/BOPTools_AlgoTools2D_1.cxx b/src/BOPTools/BOPTools_AlgoTools2D_1.cxx
index 0e713e5475..c098f90854 100644
--- a/src/BOPTools/BOPTools_AlgoTools2D_1.cxx
+++ b/src/BOPTools/BOPTools_AlgoTools2D_1.cxx
@@ -37,6 +37,7 @@
 #include <TopExp_Explorer.hxx>
 
 #include <IntTools_Context.hxx>
+#include <IntTools_Tools.hxx>
 
 #include <BOPTools_AlgoTools2D.hxx>
 
@@ -55,7 +56,6 @@ static
   Standard_Boolean IsClosed(const TopoDS_Edge& ,
                             const TopoDS_Face& );
 
-
 //=======================================================================
 //function : AttachExistingPCurve
 //purpose  : 
@@ -66,9 +66,10 @@ Standard_Integer BOPTools_AlgoTools2D::AttachExistingPCurve
    const TopoDS_Face& aF, 
    const Handle(IntTools_Context)& aCtx)
 {
-  Standard_Boolean bIsToReverse, bIsClosed;
+  Standard_Boolean bIsToReverse, bIsClosed, bComp;
   Standard_Integer iRet;
   Standard_Real aTol, aT11, aT12, aT21, aT22, aTolPPC;
+  Standard_Real aTolSP, aTMax;
   Handle(Geom2d_Curve) aC2Dold, aC2DoldC;
   Handle(Geom2d_Curve) aC2DT;
   BRep_Builder aBB;
@@ -97,13 +98,10 @@ Standard_Integer BOPTools_AlgoTools2D::AttachExistingPCurve
   //
   aC2DT=new Geom2d_TrimmedCurve(aC2DoldC, aT21, aT22);
   //
-  aTol=BRep_Tool::Tolerance(aE1);
-  BRep_Tool::Range (aE1, aT11, aT12);
-  aBB.SameRange(aE1, Standard_False);
-  aBB.SameParameter(aE1, Standard_False);
-  
   aTolPPC=Precision::PConfusion();
   //
+  Handle(Geom_Curve) aCE1 = BRep_Tool::Curve(aE1, aT11, aT12);
+  //
   GeomLib::SameRange(aTolPPC, aC2DT, aT21, aT22, aT11, aT12, aC2DT);
   //
   if (aC2DT.IsNull()){
@@ -111,15 +109,36 @@ Standard_Integer BOPTools_AlgoTools2D::AttachExistingPCurve
     return iRet;
   }
   //
+  // check the curves on same parameter to prevent 
+  // big tolerance increasing
+  Handle(Geom_Surface) aSF = BRep_Tool::Surface(aF);
+  //
+  bComp = IntTools_Tools::ComputeTolerance
+    (aCE1, aC2DT, aSF, aT11, aT12, aTolSP, aTMax);
+  if (!bComp) {
+    iRet = 3;
+    return iRet;
+  }
+  //
+  aTol = BRep_Tool::Tolerance(aE1);
+  //
+  if ((aTolSP > 10.*aTol) && aTolSP > 0.1) {
+    iRet = 4;
+    return iRet;
+  }
+  //
+  aBB.SameRange(aE1, Standard_False);
+  aBB.SameParameter(aE1, Standard_False);
+  //
   aBB.UpdateEdge(aE1, aC2DT, aF, aTol);
   BRepLib::SameParameter(aE1);
   BRepLib::SameRange(aE1);
   //
-  bIsClosed=IsClosed(aE2, aF);
+  bIsClosed = IsClosed(aE2, aF);
   if (bIsClosed) {
-    iRet=UpdateClosedPCurve(aE2, aE1, aF, aCtx);
+    iRet = UpdateClosedPCurve(aE2, aE1, aF, aCtx);
     if(iRet) {
-      iRet=3;
+      iRet = 5;
     }
   }
   //
@@ -309,4 +328,3 @@ Standard_Boolean IsClosed(const TopoDS_Edge& aE,
   }
   return bRet;
 }
-
diff --git a/tests/boolean/gdml_private/ZD3 b/tests/boolean/gdml_private/ZD3
index 362116bf4d..2f8beda78c 100644
--- a/tests/boolean/gdml_private/ZD3
+++ b/tests/boolean/gdml_private/ZD3
@@ -1,3 +1,2 @@
-puts "TODO OCC26018 Windows: Faulty shapes in variables faulty_1 to faulty_"
+puts "TODO OCC26018 ALL: Faulty shapes in variables faulty_1 to faulty_"
 source [locate_data_file 200a0-1_sopac-dn500.asm.1.gdml.tcl]
-
diff --git a/tests/boolean/gdml_private/ZD6 b/tests/boolean/gdml_private/ZD6
index ef2a429bd3..718103630a 100644
--- a/tests/boolean/gdml_private/ZD6
+++ b/tests/boolean/gdml_private/ZD6
@@ -1,2 +1,2 @@
+puts "TODO OCC26018 ALL: Faulty shapes in variables faulty_1 to faulty_"
 source [locate_data_file 200a0-1_sopac-dn500_piquage.prt.1.gdml.tcl]
-
diff --git a/tests/bugs/modalg_6/bug26718 b/tests/bugs/modalg_6/bug26718
new file mode 100755
index 0000000000..eb8e62dde5
--- /dev/null
+++ b/tests/bugs/modalg_6/bug26718
@@ -0,0 +1,45 @@
+puts "============"
+puts "OCC26718"
+puts "============"
+puts ""
+#############################################################################################
+## Big tolerance value of the edge in the result of Genral Fuse operation
+#############################################################################################
+
+restore [locate_data_file bug26718_w6_b1.brep] b1
+restore [locate_data_file bug26718_w6_b2.brep] b2
+
+bclearobjects
+bcleartools
+baddobjects b1
+baddtools b2
+
+bfillds
+bbuild result
+
+set square 2.3834e+06
+
+set nbshapes_expected "
+Number of shapes in shape
+ VERTEX    : 7
+ EDGE      : 11
+ WIRE      : 8
+ FACE      : 5
+ SHELL     : 2
+ SOLID     : 2
+ COMPSOLID : 0
+ COMPOUND  : 1
+ SHAPE     : 36
+"
+
+checknbshapes result -ref ${nbshapes_expected} -t -m "Result obtained by General Fuse operation"
+
+regexp {Tolerance +MAX=([-0-9.+eE]+)} [tolerance result] full MaxTolerance
+puts "MaxTolerance=$MaxTolerance"
+
+set expected_MaxTolerance 0.317915740714732
+set tol_abs_MaxTolerance 0.01
+set tol_rel_MaxTolerance 0.01
+checkreal "MaxTolerance" ${MaxTolerance} ${expected_MaxTolerance} ${tol_abs_MaxTolerance} ${tol_rel_MaxTolerance}
+
+set 3dviewer 1