diff --git a/pcbnew/exporters/step/exporter_step.cpp b/pcbnew/exporters/step/exporter_step.cpp
index 5b3a4b97be..64c624a153 100644
--- a/pcbnew/exporters/step/exporter_step.cpp
+++ b/pcbnew/exporters/step/exporter_step.cpp
@@ -326,7 +326,8 @@ void EXPORTER_STEP::determinePcbThickness()
             }
         }
 
-        m_boardThickness = pcbIUScale.IUTomm( thickness );
+        if( thickness > 0 )
+            m_boardThickness = pcbIUScale.IUTomm( thickness );
     }
 }