diff --git a/extflat/EFbuild.c b/extflat/EFbuild.c
index 44c9c019..09ac3a2e 100644
--- a/extflat/EFbuild.c
+++ b/extflat/EFbuild.c
@@ -167,6 +167,12 @@ efBuildNode(def, isSubsnode, nodeName, nodeCap, x, y, layerName, av, ac)
 		newnode->efnode_pa[n].pa_area += atoi(*av++);
 		newnode->efnode_pa[n].pa_perim += atoi(*av++);
 	    }
+
+	    /* If this node is identified as substrate, ensure that */
+	    /* the flag is set.					    */
+	    if (isSubsnode == TRUE)
+		newnode->efnode_flags |= EF_SUBS_NODE;
+    
 	    return;
 	}
     }