diff --git a/src/Twig/Runtime/IconRuntime.php b/src/Twig/Runtime/IconRuntime.php
index f5d679d..1179415 100644
--- a/src/Twig/Runtime/IconRuntime.php
+++ b/src/Twig/Runtime/IconRuntime.php
@@ -45,7 +45,8 @@ final class IconRuntime implements RuntimeExtensionInterface
         $options = $this->mergeWithDefaultOptions($userOptions);
 
         $svg = $this->getSvg($options['icon']);
-        $svg = $this->sanitiseSvg($svg);
+
+        $this->sanitiseSvg($svg);
 
         $colourClasses = $this->getColourClasses($options['colour'], $options['hover']);
         $extraClasses = $this->getExtraClasses($options['classes']);
@@ -93,13 +94,12 @@ final class IconRuntime implements RuntimeExtensionInterface
         return file_get_contents($iconFilepath);
     }
 
-    private function sanitiseSvg(string &$svg): string
+    private function sanitiseSvg(string &$svg): void
     {
         $this->removeExistingTitleElement($svg);
         $this->removeBlackStrokeAttributes($svg);
         $this->removeStrokeCurrentColor($svg);
-
-        return $this->removeBlackFillAttributes($svg);
+        $this->removeBlackFillAttributes($svg);
     }
 
     private function findSvgFilepath(string $iconName): string
@@ -130,9 +130,9 @@ final class IconRuntime implements RuntimeExtensionInterface
         $svg = \preg_replace('/stroke=(\'|")currentColor(\'|")/', '', $svg);
     }
 
-    private function removeBlackFillAttributes(string $content): string
+    private function removeBlackFillAttributes(string &$svg): void
     {
-        return preg_replace('/fill(=|:)"?\s*(#0{6}|#000|rgb\(\s*0,\s*0,\s*0\s*\)|black)\s*"?/', '', $content);
+        $svg = preg_replace('/fill(=|:)"?\s*(#0{6}|#000|rgb\(\s*0,\s*0,\s*0\s*\)|black)\s*"?/', '', $svg);
     }
 
     private function getColourClasses(string $primaryColour, ?string $hoverColour): string