diff --git a/pcbnew/connectivity_algo.cpp b/pcbnew/connectivity_algo.cpp
index 6562a3f2e9..bacdc40ef9 100644
--- a/pcbnew/connectivity_algo.cpp
+++ b/pcbnew/connectivity_algo.cpp
@@ -932,8 +932,18 @@ void CN_CONNECTIVITY_ALGO::MarkNetAsDirty( int aNet )
         return;
 
     if( (int) m_dirtyNets.size() <= aNet )
+    {
+        int lastNet = m_dirtyNets.size() - 1;
+
+        if( lastNet < 0 )
+            lastNet = 0;
+
         m_dirtyNets.resize( aNet + 1 );
 
+        for( int i = lastNet; i < aNet + 1; i++ )
+            m_dirtyNets[i] = true;
+    }
+
     m_dirtyNets[aNet] = true;
 }