diff --git a/lib/classes/chart_base.php b/lib/classes/chart_base.php
index 14ff5998f83f6..74ff7b365da1a 100644
--- a/lib/classes/chart_base.php
+++ b/lib/classes/chart_base.php
@@ -237,7 +237,7 @@ public function set_title($title) {
      * @param int $index The index of the axis.
      */
     public function set_xaxis(chart_axis $axis, $index = 0) {
-        $this->validateAxis('x', $axis, $index);
+        $this->validate_axis('x', $axis, $index);
         return $this->xaxes[$index] = $axis;
     }
 
@@ -250,7 +250,7 @@ public function set_xaxis(chart_axis $axis, $index = 0) {
      * @param int $index The index of the axis.
      */
     public function set_yaxis(chart_axis $axis, $index = 0) {
-        $this->validateAxis('y', $axis, $index);
+        $this->validate_axis('y', $axis, $index);
         return $this->yaxes[$index] = $axis;
     }
 
@@ -266,7 +266,7 @@ public function set_yaxis(chart_axis $axis, $index = 0) {
      * @param chart_axis $axis The axis to validate.
      * @param index $index The index of the axis.
      */
-    protected function validateAxis($xy, chart_axis $axis, $index = 0) {
+    protected function validate_axis($xy, chart_axis $axis, $index = 0) {
         if ($index > 0) {
             $axes = $xy == 'x' ? $this->xaxes : $this->yaxes;
             if (!isset($axes[$index - 1])) {