diff --git a/Algorithm/Clustering/PointInterface.php b/Algorithm/Clustering/PointInterface.php
index 02a258d71..2c0fb850b 100644
--- a/Algorithm/Clustering/PointInterface.php
+++ b/Algorithm/Clustering/PointInterface.php
@@ -28,7 +28,7 @@ interface PointInterface
     /**
      * Get the point coordinates
      *
-     * @return array
+     * @return array<int, int|float>
      *
      * @since 1.0.0
      */
@@ -37,25 +37,25 @@ interface PointInterface
     /**
      * Get the coordinate of the point
      *
-     * @param mixed $index Index of the coordinate (e.g. 0 = x);
+     * @param int $index Index of the coordinate (e.g. 0 = x);
      *
      * @return int|float
      *
      * @since 1.0.0
      */
-    public function getCoordinate($index);
+    public function getCoordinate(int $index);
 
     /**
      * Set the coordinate of the point
      *
-     * @param mixed $index Index of the coordinate (e.g. 0 = x);
+     * @param int $index Index of the coordinate (e.g. 0 = x);
      * @param mixed $value Value of the coordinate
      *
      * @return void
      *
      * @since 1.0.0
      */
-    public function setCoordinate($index, $value) : void;
+    public function setCoordinate(int $index, $value) : void;
 
     /**
      * Get group this point belongs to