diff --git a/pcbnew/router/pns_kicad_iface.cpp b/pcbnew/router/pns_kicad_iface.cpp
index 9614dcb75d..e33f983b3e 100644
--- a/pcbnew/router/pns_kicad_iface.cpp
+++ b/pcbnew/router/pns_kicad_iface.cpp
@@ -128,6 +128,7 @@ public:
     int ClearanceEpsilon() const { return m_clearanceEpsilon; }
 
     void ClearCacheForItem( const PNS::ITEM* aItem ) override;
+    void ClearCaches() override;
 
 private:
     int holeRadius( const PNS::ITEM* aItem ) const;
@@ -377,6 +378,14 @@ void PNS_PCBNEW_RULE_RESOLVER::ClearCacheForItem( const PNS::ITEM* aItem )
 }
 
 
+void PNS_PCBNEW_RULE_RESOLVER::ClearCaches()
+{
+    m_clearanceCache.clear();
+    m_holeClearanceCache.clear();
+    m_holeToHoleClearanceCache.clear();
+}
+
+
 int PNS_PCBNEW_RULE_RESOLVER::Clearance( const PNS::ITEM* aA, const PNS::ITEM* aB,
                                          bool aUseClearanceEpsilon )
 {
diff --git a/pcbnew/router/pns_node.cpp b/pcbnew/router/pns_node.cpp
index 60a591fd7f..a62c956ad8 100644
--- a/pcbnew/router/pns_node.cpp
+++ b/pcbnew/router/pns_node.cpp
@@ -307,6 +307,10 @@ NODE::OPT_OBSTACLE NODE::NearestObstacle( const LINE* aLine, int aKindMask,
 
     for( int i = 0; i < aLine->CLine().SegmentCount(); i++ )
     {
+        // Note: Clearances between &s and other items are cached,
+        // which means they'll be the same for all segments in the line.
+        // Disabling the cache will lead to slowness.
+
         const SEGMENT s( *aLine, aLine->CLine().CSegment( i ) );
         QueryColliding( &s, obstacleList, aKindMask );
     }
@@ -479,6 +483,10 @@ NODE::OPT_OBSTACLE NODE::CheckColliding( const ITEM* aItemA, int aKindMask )
 
         for( int i = 0; i < l.SegmentCount(); i++ )
         {
+            // Note: Clearances between &s and other items are cached,
+            // which means they'll be the same for all segments in the line.
+            // Disabling the cache will lead to slowness.
+
             const SEGMENT s( *line, l.CSegment( i ) );
             n += QueryColliding( &s, obs, aKindMask, 1 );
 
@@ -489,7 +497,7 @@ NODE::OPT_OBSTACLE NODE::CheckColliding( const ITEM* aItemA, int aKindMask )
         if( line->EndsWithVia() )
         {
             n += QueryColliding( &line->Via(), obs, aKindMask, 1 );
-            
+
             if( n )
                 return OPT_OBSTACLE( obs[0] );
         }
diff --git a/pcbnew/router/pns_node.h b/pcbnew/router/pns_node.h
index 27681fa3e5..fb197c2335 100644
--- a/pcbnew/router/pns_node.h
+++ b/pcbnew/router/pns_node.h
@@ -103,6 +103,7 @@ public:
     virtual wxString NetName( int aNet ) = 0;
 
     virtual void ClearCacheForItem( const ITEM* aItem ) {}
+    virtual void ClearCaches() {}
 };
 
 /**
diff --git a/pcbnew/router/pns_router.cpp b/pcbnew/router/pns_router.cpp
index 1883858e7a..039b1a4632 100644
--- a/pcbnew/router/pns_router.cpp
+++ b/pcbnew/router/pns_router.cpp
@@ -166,6 +166,8 @@ bool ROUTER::StartDragging( const VECTOR2I& aP, ITEM_SET aStartItems, int aDragM
         m_world->SetCollisionQueryScope( NODE::CQS_IGNORE_HOLE_CLEARANCE );
     }
 
+    GetRuleResolver()->ClearCaches();
+
     if( aStartItems.Count( ITEM::SOLID_T ) == aStartItems.Size() )
     {
         m_dragger = std::make_unique<COMPONENT_DRAGGER>( this );
@@ -396,6 +398,8 @@ bool ROUTER::StartRouting( const VECTOR2I& aP, ITEM* aStartItem, int aLayer )
         m_world->SetCollisionQueryScope( NODE::CQS_IGNORE_HOLE_CLEARANCE );
     }
 
+    GetRuleResolver()->ClearCaches();
+
     if( !isStartingPointRoutable( aP, aStartItem, aLayer ) )
         return false;
 
@@ -790,7 +794,7 @@ bool ROUTER::GetUpdatedItems( std::vector<PNS::ITEM*>& aRemoved, std::vector<PNS
     }
 
     tmpNode->GetUpdatedItems( aRemoved, aAdded );
-    
+
     //printf("added %d removed %d\n", aRemoved.size(), aAdded.size() );
 
     return true;