diff -urp a/src/rrd_graph_helper.c b/src/rrd_graph_helper.c
--- a/src/rrd_graph_helper.c	2016-04-19 17:52:25.000000000 +0200
+++ b/src/rrd_graph_helper.c	2019-05-14 15:46:53.476975477 +0200
@@ -532,7 +532,7 @@ static graph_desc_t* newGraphDescription
     double linewidth = 1;
     char *t,*x;
     if ((t=getKeyValueArgument("linewidth",1,pa))&&(*t!=0)) {
-      if ((getDouble(t,&linewidth,&x))||(linewidth<=0)) {
+      if ((getDouble(t,&linewidth,&x))||(linewidth<0)) {
 	rrd_set_error("Bad line width: %s",t); return NULL;
       }
     }