diff --git a/libs/kimath/include/geometry/shape_line_chain.h b/libs/kimath/include/geometry/shape_line_chain.h
index dc266c3d9f..68cbb9b003 100644
--- a/libs/kimath/include/geometry/shape_line_chain.h
+++ b/libs/kimath/include/geometry/shape_line_chain.h
@@ -628,9 +628,10 @@ public:
      * Function Simplify()
      *
      * Simplifies the line chain by removing colinear adjacent segments and duplicate vertices.
+     * @param aRemoveColinear controsl the removal of colinear adjacent segments
      * @return reference to self.
      */
-    SHAPE_LINE_CHAIN& Simplify();
+    SHAPE_LINE_CHAIN& Simplify( bool aRemoveColinear = true );
 
     /**
      * Converts an arc to only a point chain by removing the arc and references
@@ -747,7 +748,14 @@ public:
 
     bool isArc( size_t aSegment ) const
     {
-        return aSegment < m_shapes.size() && m_shapes[aSegment] != SHAPE_IS_PT;
+        /**
+         * A segment is part of an arc except in the special case of two arcs next to each other
+         * but without a shared vertex.  Here there is a segment between the end of the first arc
+         * and the start of the second arc.
+         */
+        return ( aSegment < m_shapes.size() - 1
+                 && m_shapes[aSegment] != SHAPE_IS_PT
+                 && m_shapes[aSegment] == m_shapes[aSegment + 1] );
     }
 
     virtual const VECTOR2I GetPoint( int aIndex ) const override { return CPoint(aIndex); }
diff --git a/libs/kimath/src/geometry/shape_line_chain.cpp b/libs/kimath/src/geometry/shape_line_chain.cpp
index f5ce62450c..fb45c43fc2 100644
--- a/libs/kimath/src/geometry/shape_line_chain.cpp
+++ b/libs/kimath/src/geometry/shape_line_chain.cpp
@@ -936,7 +936,7 @@ const OPT<SHAPE_LINE_CHAIN::INTERSECTION> SHAPE_LINE_CHAIN::SelfIntersecting() c
 }
 
 
-SHAPE_LINE_CHAIN& SHAPE_LINE_CHAIN::Simplify()
+SHAPE_LINE_CHAIN& SHAPE_LINE_CHAIN::Simplify( bool aRemoveColinear )
 {
     std::vector<VECTOR2I> pts_unique;
     std::vector<ssize_t> shapes_unique;
@@ -961,11 +961,25 @@ SHAPE_LINE_CHAIN& SHAPE_LINE_CHAIN::Simplify()
     {
         int j = i + 1;
 
-        while( j < np && m_points[i] == m_points[j] && m_shapes[i] == m_shapes[j] )
+        // We can eliminate duplicate vertices as long as they are part of the same shape, OR if
+        // one of them is part of a shape and one is not.
+        while( j < np && m_points[i] == m_points[j] &&
+               ( m_shapes[i] == m_shapes[j] ||
+                 m_shapes[i] == SHAPE_IS_PT ||
+                 m_shapes[j] == SHAPE_IS_PT ) )
+        {
             j++;
+        }
+
+        int shapeToKeep = m_shapes[i];
+
+        if( shapeToKeep == SHAPE_IS_PT )
+            shapeToKeep = m_shapes[j - 1];
+
+        wxASSERT( shapeToKeep < static_cast<int>( m_arcs.size() ) );
 
         pts_unique.push_back( CPoint( i ) );
-        shapes_unique.push_back( m_shapes[i] );
+        shapes_unique.push_back( shapeToKeep );
 
         i = j;
     }
@@ -976,17 +990,20 @@ SHAPE_LINE_CHAIN& SHAPE_LINE_CHAIN::Simplify()
 
     i = 0;
 
-    // stage 1: eliminate collinear segments
+    // stage 2: eliminate colinear segments
     while( i < np - 2 )
     {
         const VECTOR2I p0 = pts_unique[i];
         const VECTOR2I p1 = pts_unique[i + 1];
         int n = i;
 
-        while( n < np - 2
-                && ( SEG( p0, p1 ).LineDistance( pts_unique[n + 2] ) <= 1
-                        || SEG( p0, p1 ).Collinear( SEG( p1, pts_unique[n + 2] ) ) ) )
-            n++;
+        if( aRemoveColinear )
+        {
+            while( n < np - 2
+                    && ( SEG( p0, p1 ).LineDistance( pts_unique[n + 2] ) <= 1
+                            || SEG( p0, p1 ).Collinear( SEG( p1, pts_unique[n + 2] ) ) ) )
+                n++;
+        }
 
         m_points.push_back( p0 );
         m_shapes.push_back( shapes_unique[i] );
diff --git a/pcbnew/router/pns_line_placer.cpp b/pcbnew/router/pns_line_placer.cpp
index 1f9ad4dddf..31ce47d8e9 100644
--- a/pcbnew/router/pns_line_placer.cpp
+++ b/pcbnew/router/pns_line_placer.cpp
@@ -1111,9 +1111,10 @@ bool LINE_PLACER::FixRoute( const VECTOR2I& aP, ITEM* aEndItem, bool aForceFinis
     else
         lastV = std::max( 1, l.SegmentCount() - 1 );
 
-    SEGMENT  seg;
-    SEGMENT* lastSeg = nullptr;
-    int      lastArc = -1;
+    ARC          arc;
+    SEGMENT      seg;
+    LINKED_ITEM* lastItem = nullptr;
+    int          lastArc  = -1;
 
     for( int i = 0; i < lastV; i++ )
     {
@@ -1126,27 +1127,28 @@ bool LINE_PLACER::FixRoute( const VECTOR2I& aP, ITEM* aEndItem, bool aForceFinis
             seg.SetLayer( m_currentLayer );
 
             if( m_lastNode->Add( std::make_unique<SEGMENT>( seg ) ) )
-                lastSeg = &seg;
+                lastItem = &seg;
         }
         else
         {
             if( arcIndex == lastArc )
                 continue;
 
-            std::unique_ptr<ARC> arc = std::make_unique<ARC>( l.Arc( arcIndex ), m_currentNet );
-            arc->SetWidth( pl.Width() );
-            arc->SetLayer( m_currentLayer );
-            m_lastNode->Add( std::move( arc ) );
-            lastSeg = nullptr;
-            lastArc = arcIndex;
+            arc = ARC( l.Arc( arcIndex ), m_currentNet );
+            arc.SetWidth( pl.Width() );
+            arc.SetLayer( m_currentLayer );
+
+            m_lastNode->Add( std::make_unique<ARC>( arc ) );
+            lastItem = &arc;
+            lastArc  = arcIndex;
         }
     }
 
     if( pl.EndsWithVia() )
         m_lastNode->Add( Clone( pl.Via() ) );
 
-    if( realEnd && lastSeg )
-        simplifyNewLine( m_lastNode, lastSeg );
+    if( realEnd && lastItem )
+        simplifyNewLine( m_lastNode, lastItem );
 
     if( !realEnd )
     {
@@ -1297,8 +1299,9 @@ void LINE_PLACER::removeLoops( NODE* aNode, LINE& aLatest )
 }
 
 
-void LINE_PLACER::simplifyNewLine( NODE* aNode, SEGMENT* aLatest )
+void LINE_PLACER::simplifyNewLine( NODE* aNode, LINKED_ITEM* aLatest )
 {
+    wxASSERT( aLatest->OfKind( ITEM::SEGMENT_T | ITEM::ARC_T ) );
     LINE l = aNode->AssembleLine( aLatest );
 
     bool optimized = OPTIMIZER::Optimize( &l, OPTIMIZER::MERGE_COLINEAR, aNode );
diff --git a/pcbnew/router/pns_line_placer.h b/pcbnew/router/pns_line_placer.h
index d4eaddb669..15215d9f5f 100644
--- a/pcbnew/router/pns_line_placer.h
+++ b/pcbnew/router/pns_line_placer.h
@@ -320,13 +320,11 @@ private:
     void removeLoops( NODE* aNode, LINE& aLatest );
 
     /**
-     * Function simplifyNewLine()
-     *
-     * Assembles a line starting from segment aLatest, removes collinear segments
+     * Assembles a line starting from segment or arc aLatest, removes collinear segments
      * and redundant vertexes. If a simplification bhas been found, replaces the
      * old line with the simplified one in aNode.
      */
-    void simplifyNewLine( NODE* aNode, SEGMENT* aLatest );
+    void simplifyNewLine( NODE* aNode, LINKED_ITEM* aLatest );
 
     /**
      * Function handleSelfIntersections()
diff --git a/pcbnew/router/pns_node.cpp b/pcbnew/router/pns_node.cpp
index 9d32f21226..09d4dac373 100644
--- a/pcbnew/router/pns_node.cpp
+++ b/pcbnew/router/pns_node.cpp
@@ -958,7 +958,8 @@ const LINE NODE::AssembleLine( LINKED_ITEM* aSeg, int* aOriginSegmentIndex,
         prev_seg = li;
     }
 
-    pl.Line().Simplify();
+    // Remove duplicate verts, but do NOT remove colinear segments here!
+    pl.Line().Simplify( false );
 
     assert( pl.SegmentCount() != 0 );