diff --git a/SurfRoughing.cpp b/SurfRoughing.cpp
index 0a48eee..3c0d0c2 100644
--- a/SurfRoughing.cpp
+++ b/SurfRoughing.cpp
@@ -1371,7 +1371,7 @@ SurfRoughing::ProcessPath( int nPathId, int nPvId, int nClId)
       double dOkSubStep = -1. ;
       int nSubStep = -1 ;
       double dSubStep = -1. ;
-      if ( m_Params.m_dSubStep > EPS_SMALL  &&  m_Params.m_dSubStep < m_Params.m_dStep) {
+      if ( m_Params.m_dSubStep > EPS_SMALL  &&  m_Params.m_dSubStep < m_Params.m_dStep  &&  dDepth > m_Params.m_dSubStep) {
          dOkSubStep = min( m_Params.m_dSubStep, m_TParams.m_dMaxMat + EPS_SMALL) ;
          nSubStep = nStep * max( 1, static_cast<int>( ceil( dOkStep / dOkSubStep))) ;
          dSubStep = dDepth / nSubStep ;