diff --git a/htdocs/core/class/dolgraph.class.php b/htdocs/core/class/dolgraph.class.php
index 37f1d6036c6..5b477ace9c8 100644
--- a/htdocs/core/class/dolgraph.class.php
+++ b/htdocs/core/class/dolgraph.class.php
@@ -899,7 +899,10 @@ class DolGraph
 		}
 
 		$legends=array();
-		$nblot=count($this->data[0])-1;    // -1 to remove legend
+		$nblot=0;
+		if (is_array($this->data) && is_array($this->data[0])) {
+			$nblot=count($this->data[0])-1;    // -1 to remove legend
+		}
 		if ($nblot < 0) dol_syslog('Bad value for property ->data. Must be set by mydolgraph->SetData before calling mydolgrapgh->draw', LOG_WARNING);
 		$firstlot=0;
 		// Works with line but not with bars