diff --git a/lib/Sabberworm/CSS/Value/Size.php b/lib/Sabberworm/CSS/Value/Size.php
index 8490cc35..cd1a213c 100644
--- a/lib/Sabberworm/CSS/Value/Size.php
+++ b/lib/Sabberworm/CSS/Value/Size.php
@@ -3,12 +3,13 @@
 namespace Sabberworm\CSS\Value;
 
 use Sabberworm\CSS\Parsing\ParserState;
+use Sabberworm\CSS\Parsing\UnexpectedTokenException;
 
 class Size extends PrimitiveValue {
 
 	const ABSOLUTE_SIZE_UNITS = 'px/cm/mm/mozmm/in/pt/pc/vh/vw/vmin/vmax/rem'; //vh/vw/vm(ax)/vmin/rem are absolute insofar as they don’t scale to the immediate parent (only the viewport)
 	const RELATIVE_SIZE_UNITS = '%/em/ex/ch/fr';
-	const NON_SIZE_UNITS = 'deg/grad/rad/s/ms/turns/Hz/kHz';
+	const NON_SIZE_UNITS = 'deg/grad/rad/s/ms/turn/Hz/kHz';
 
 	private static $SIZE_UNITS = null;
 
@@ -38,15 +39,20 @@ public static function parse(ParserState $oParserState, $bIsColorComponent = fal
 
 		$sUnit = null;
 		$aSizeUnits = self::getSizeUnits();
-		foreach($aSizeUnits as $iLength => &$aValues) {
-			$sKey = strtolower($oParserState->peek($iLength));
-			if(array_key_exists($sKey, $aValues)) {
-				if (($sUnit = $aValues[$sKey]) !== null) {
-					$oParserState->consume($iLength);
-					break;
-				}
+		$iMaxSizeUnitLength = max(array_keys($aSizeUnits));
+
+		if ( preg_match( '/^(%|[a-zA-Z0-9]+)/', $oParserState->peek($iMaxSizeUnitLength), $matches ) ) {
+			$sUnit = strtolower($matches[0]);
+			$iUnitLength = strlen($sUnit);
+
+			if (isset($aSizeUnits[$iUnitLength][$sUnit])) {
+				$sUnit = $aSizeUnits[$iUnitLength][$sUnit];
+				$oParserState->consume($iUnitLength);
+			} else {
+				throw new UnexpectedTokenException('Unit', $sUnit, 'identifier', $oParserState->currentLine());
 			}
 		}
+
 		return new Size(floatval($sSize), $sUnit, $bIsColorComponent, $oParserState->currentLine());
 	}
 
diff --git a/tests/Sabberworm/CSS/ParserTest.php b/tests/Sabberworm/CSS/ParserTest.php
index 4a690196..6ef74bbb 100644
--- a/tests/Sabberworm/CSS/ParserTest.php
+++ b/tests/Sabberworm/CSS/ParserTest.php
@@ -787,4 +787,22 @@ function testLonelyImport() {
 		$sExpected = "@import url(\"example.css\") only screen and (max-width: 600px);";
 		$this->assertSame($sExpected, $oDoc->render());
 	}
+
+	function testTurnUnitLenient() {
+		$sText = ".foo {transform: rotate(1turn);}\n.bar {transform: rotate(1turns);}";
+		$sExpected = ".foo {transform: rotate(1turn);}\n.bar {}";
+
+		$oParser = new Parser($sText);
+		$this->assertSame($sExpected, $oParser->parse()->render());
+	}
+
+	function testTurnUnitStrict() {
+		$sText = ".foo {transform: rotate(1turn);}\n.bar {transform: rotate(1turns);}";
+
+		$oParser = new Parser($sText, Settings::create()->beStrict());
+
+		// Line 2 contains the invalid unit and so should be reported.
+		$this->setExpectedException( 'Sabberworm\CSS\Parsing\UnexpectedTokenException', 'Identifier expected. Got “turns” [line no: 2]' );
+		$oParser->parse();
+	}
 }