diff --git a/src/BlockFix/BlockFix_UnionFaces.cxx b/src/BlockFix/BlockFix_UnionFaces.cxx
index 15ed9da9b..294deb224 100644
--- a/src/BlockFix/BlockFix_UnionFaces.cxx
+++ b/src/BlockFix/BlockFix_UnionFaces.cxx
@@ -91,6 +91,7 @@
 #include <Bnd_Box.hxx>
 #include <BRepBndLib.hxx>
 
+#include <Geom_TrimmedCurve.hxx>
 #include <Geom_Curve.hxx>
 #include <Geom_Line.hxx>
 #include <Geom_Circle.hxx>
@@ -814,6 +815,13 @@ bool getCylinder (Handle(Geom_Surface)& theInSurface, gp_Cylinder& theOutCylinde
     Handle(Geom_SurfaceOfRevolution) aRS =
       Handle(Geom_SurfaceOfRevolution)::DownCast(theInSurface);
     Handle(Geom_Curve) aBasis = aRS->BasisCurve();
+
+    while (aBasis->IsKind(STANDARD_TYPE(Geom_TrimmedCurve))) {
+      Handle(Geom_TrimmedCurve) aTc =
+        Handle(Geom_TrimmedCurve)::DownCast(aBasis);
+      aBasis = aTc->BasisCurve();
+    }
+
     if (aBasis->IsKind(STANDARD_TYPE(Geom_Line))) {
       Handle(Geom_Line) aBasisLine = Handle(Geom_Line)::DownCast(aBasis);
       gp_Dir aDir = aRS->Direction();
@@ -833,6 +841,13 @@ bool getCylinder (Handle(Geom_Surface)& theInSurface, gp_Cylinder& theOutCylinde
     Handle(Geom_SurfaceOfLinearExtrusion) aLES =
       Handle(Geom_SurfaceOfLinearExtrusion)::DownCast(theInSurface);
     Handle(Geom_Curve) aBasis = aLES->BasisCurve();
+
+    while (aBasis->IsKind(STANDARD_TYPE(Geom_TrimmedCurve))) {
+      Handle(Geom_TrimmedCurve) aTc =
+        Handle(Geom_TrimmedCurve)::DownCast(aBasis);
+      aBasis = aTc->BasisCurve();
+    }
+
     if (aBasis->IsKind(STANDARD_TYPE(Geom_Circle))) {
       Handle(Geom_Circle) aBasisCircle = Handle(Geom_Circle)::DownCast(aBasis);
       gp_Dir aDir = aLES->Direction();