diff --git a/pcbnew/zone.cpp b/pcbnew/zone.cpp
index ce3b92113d..55caca755a 100644
--- a/pcbnew/zone.cpp
+++ b/pcbnew/zone.cpp
@@ -1056,7 +1056,7 @@ bool ZONE::BuildSmoothedPoly( SHAPE_POLY_SET& aSmoothedPoly, PCB_LAYER_ID aLayer
         return false;
 
     // Processing of arc shapes in zones is not yet supported because Clipper can't do boolean
-    // operations on them.  The poly outline must be flattened first.
+    // operations on them.  The poly outline must be converted to segments first.
     SHAPE_POLY_SET flattened = *m_Poly;
     flattened.ClearArcs();
 
diff --git a/pcbnew/zone_filler.cpp b/pcbnew/zone_filler.cpp
index a27626d01e..5d3aa91e93 100644
--- a/pcbnew/zone_filler.cpp
+++ b/pcbnew/zone_filler.cpp
@@ -936,7 +936,15 @@ void ZONE_FILLER::subtractHigherPriorityZones( const ZONE* aZone, PCB_LAYER_ID a
                     return;
 
                 if( aKnockout->GetCachedBoundingBox().Intersects( aZone->GetCachedBoundingBox() ) )
-                    aRawFill.BooleanSubtract( *aKnockout->Outline(), SHAPE_POLY_SET::PM_FAST );
+                {
+                    // Processing of arc shapes in zones is not yet supported because Clipper
+                    // can't do boolean operations on them.  The poly outline must be converted to
+                    // segments first.
+                    SHAPE_POLY_SET outline = *aKnockout->Outline();
+                    outline.ClearArcs();
+
+                    aRawFill.BooleanSubtract( outline, SHAPE_POLY_SET::PM_FAST );
+                }
             };
 
     for( ZONE* otherZone : m_board->Zones() )