diff --git a/src/Extrema/Extrema_ExtSS.cxx b/src/Extrema/Extrema_ExtSS.cxx
index 88b32de34f..bf6451a64d 100644
--- a/src/Extrema/Extrema_ExtSS.cxx
+++ b/src/Extrema/Extrema_ExtSS.cxx
@@ -106,7 +106,7 @@ void Extrema_ExtSS::Perform(const Adaptor3d_Surface&   S1,
   mySqDist.Clear();
   Standard_Integer i;
   GeomAbs_SurfaceType myS1type  = S1.GetType();
-  Standard_Integer NbU = 10, NbV = 10;
+  const Standard_Integer NbU = 20, NbV = 20;
   
   switch(myS1type) {
 
diff --git a/tests/bugs/modalg_6/bug27981 b/tests/bugs/modalg_6/bug27981
new file mode 100644
index 0000000000..14b68ef5f3
--- /dev/null
+++ b/tests/bugs/modalg_6/bug27981
@@ -0,0 +1,17 @@
+puts "========"
+puts "OCC27981"
+puts "========"
+puts ""
+#################################################
+# BRepExtrema_DistShapeShape returns not null distance on interfered shapes
+#################################################
+
+restore [locate_data_file bug27981_a.brep] a
+restore [locate_data_file bug27981_b.brep] b
+
+distmini dd a b
+set dist [dval dd_val]
+if {$dist > 1.e-7} {
+  puts "\nError: invalid distance.\n"
+}
+