diff --git a/htdocs/includes/tecnickcom/tcpdf/tcpdf.php b/htdocs/includes/tecnickcom/tcpdf/tcpdf.php
index 5fc00e57f75..70af2dc0f3e 100644
--- a/htdocs/includes/tecnickcom/tcpdf/tcpdf.php
+++ b/htdocs/includes/tecnickcom/tcpdf/tcpdf.php
@@ -7460,7 +7460,7 @@ class TCPDF
 						$color = imagecolorat($img, $xpx, $ypx);
 						// get and correct gamma color
 						$alpha = $this->getGDgamma($img, $color);
-						imagesetpixel($imgalpha, $xpx, $ypx, $alpha);
+						imagesetpixel($imgalpha, $xpx, $ypx, (int)$alpha);
 					}
 				}
 				imagepng($imgalpha, $tempfile_alpha);