diff --git a/src/Mpdf.php b/src/Mpdf.php
index 523b8b7d6..058ec598d 100644
--- a/src/Mpdf.php
+++ b/src/Mpdf.php
@@ -18830,9 +18830,10 @@ function setCSS($arrayaux, $type = '', $tag = '')
 
 
 				case 'FONT-VARIANT-POSITION':
-					if (isset($this->OTLtags['Plus'])) {
-						$this->OTLtags['Plus'] = str_replace(['sups', 'subs'], '', $this->OTLtags['Plus']);
+					if (!isset($this->OTLtags['Plus'])) {
+						$this->OTLtags['Plus'] = '';
 					}
+					$this->OTLtags['Plus'] = str_replace(['sups', 'subs'], '', $this->OTLtags['Plus']);
 					switch (strtoupper($v)) {
 						case 'SUPER':
 							$this->OTLtags['Plus'] .= ' sups';
diff --git a/tests/Mpdf/FontVariantPositionTest.php b/tests/Mpdf/FontVariantPositionTest.php
new file mode 100644
index 000000000..9377f54e4
--- /dev/null
+++ b/tests/Mpdf/FontVariantPositionTest.php
@@ -0,0 +1,38 @@
+<?php
+
+namespace Mpdf;
+
+class FontVariantPositionTest extends \Yoast\PHPUnitPolyfills\TestCases\TestCase
+{
+
+	/**
+	 * FreeSerif carries the sups and subs GSUB features, so each keyword has to reach the text
+	 * as a different glyph. Rendered in one document the subset ids are comparable.
+	 */
+	public function testKeywordsSelectDistinctGlyphs()
+	{
+		$mpdf = new Mpdf(['default_font' => 'freeserif']);
+		$mpdf->compress = false;
+
+		$mpdf->WriteHTML(
+			'<span style="font-variant-position: super">1</span>'
+			. '<span style="font-variant-position: sub">1</span>'
+			. '<span style="font-variant-position: normal">1</span>'
+		);
+
+		$output = $mpdf->OutputBinaryData();
+		$mpdf->cleanup();
+
+		preg_match_all('/<([0-9a-fA-F]+)>\s*Tj/', $output, $matches);
+
+		$this->assertCount(3, $matches[1], 'Expected one text-showing operator per span');
+
+		list($super, $sub, $normal) = $matches[1];
+
+		$this->assertSame('31', $normal, 'font-variant-position: normal must leave the digit alone');
+		$this->assertNotSame($normal, $super, 'font-variant-position: super must substitute the glyph');
+		$this->assertNotSame($normal, $sub, 'font-variant-position: sub must substitute the glyph');
+		$this->assertNotSame($super, $sub, 'sups and subs must not resolve to the same glyph');
+	}
+
+}