diff --git a/scss.inc.php b/scss.inc.php
index b3bfc5b0..93b6d1bd 100644
--- a/scss.inc.php
+++ b/scss.inc.php
@@ -1868,7 +1868,7 @@ public function toRGB($hue, $saturation, $lightness) {
 	protected static $lib_if = array("condition", "if-true", "if-false");
 	protected function lib_if($args) {
 		list($cond,$t, $f) = $args;
-		if ($cond == self::$false) return $f;
+		if (!$this->isTruthy($cond)) return $f;
 		return $t;
 	}
 
diff --git a/tests/inputs/if_on_null.scss b/tests/inputs/if_on_null.scss
new file mode 100644
index 00000000..ff729e74
--- /dev/null
+++ b/tests/inputs/if_on_null.scss
@@ -0,0 +1,8 @@
+@function testfunc($pseudo: null) {
+  $output: if($pseudo, "green", "red");
+  @return $output;
+}
+
+body {
+  background-color: testfunc();
+}
\ No newline at end of file
diff --git a/tests/outputs/if_on_null.css b/tests/outputs/if_on_null.css
new file mode 100644
index 00000000..2dfca956
--- /dev/null
+++ b/tests/outputs/if_on_null.css
@@ -0,0 +1,2 @@
+body {
+  background-color: "red"; }