diff --git a/src/IntPatch/IntPatch_ImpImpIntersection_4.gxx b/src/IntPatch/IntPatch_ImpImpIntersection_4.gxx
index 2e1caa95d8..b2582bd52f 100644
--- a/src/IntPatch/IntPatch_ImpImpIntersection_4.gxx
+++ b/src/IntPatch/IntPatch_ImpImpIntersection_4.gxx
@@ -2452,8 +2452,9 @@ void WorkWithBoundaries::BoundaryEstimation(const gp_Cylinder& theCy1,
   //projections of two opposite parallelogram vertices
   //(joined by the maximal diagonal) to the cylinder axis.
   const Standard_Real aSinA = sqrt(aSqSinA);
-  const Standard_Real aHDV1 = (aR1 * aCosA + aR2)/aSinA,
-                      aHDV2 = (aR2 * aCosA + aR1)/aSinA;
+  const Standard_Real anAbsCosA = Abs(aCosA);
+  const Standard_Real aHDV1 = (aR1 * anAbsCosA + aR2) / aSinA,
+                      aHDV2 = (aR2 * anAbsCosA + aR1) / aSinA;
 
 #ifdef INTPATCH_IMPIMPINTERSECTION_DEBUG
   //The code in this block is created for test only.It is stupidly to create
diff --git a/tests/bugs/modalg_6/bug28009_1 b/tests/bugs/modalg_6/bug28009_1
new file mode 100644
index 0000000000..a71eb2c0a8
--- /dev/null
+++ b/tests/bugs/modalg_6/bug28009_1
@@ -0,0 +1,27 @@
+puts "================"
+puts "OCC28009"
+puts "================"
+puts ""
+#######################################################################
+# [Regression vs OCCT7.0.0] Cut produces not valid shape
+#######################################################################
+
+restore [locate_data_file bug28009_shape.brep] a
+
+explode a
+bcut result a_1 a_2
+
+# Check result validity.
+checkshape result
+
+# Check number of topological entities in the result.
+checknbshapes result -solid 1 -shell 1 -face 12 -wire 12 -edge 28 -vertex 17
+
+# Check result area.
+checkprops result -s 4347.99
+
+smallview
+don result
+fit
+
+checkview -screenshot -2d -path ${imagedir}/${test_image}.png
diff --git a/tests/bugs/modalg_6/bug28009_2 b/tests/bugs/modalg_6/bug28009_2
new file mode 100644
index 0000000000..f5b68179a0
--- /dev/null
+++ b/tests/bugs/modalg_6/bug28009_2
@@ -0,0 +1,31 @@
+puts "================"
+puts "OCC28009"
+puts "================"
+puts ""
+#######################################################################
+# [Regression vs OCCT7.0.0] Cut produces not valid shape
+#######################################################################
+
+set NbCurvGood 1
+set ExpToler 9.0002189481237598e-008
+
+restore [locate_data_file bug28009_shape.brep] a
+
+explode a
+
+explode a_1 f
+explode a_2 f
+
+regexp {Tolerance Reached=+([-0-9.+eE]+)\n+([-0-9.+eE]+)} [bopcurves a_1_6 a_2_1 -2d] full Toler NbCurv
+if {${NbCurv} != 1} {
+  puts "Error: Number of curves is bad!"
+}
+
+checkreal TolReached $Toler $ExpToler 0.0 0.1
+
+smallview
+don c_*
+fit
+display a_1_6 a_2_1
+
+checkview -screenshot -2d -path ${imagedir}/${test_image}.png