diff --git a/lib/Sabberworm/CSS/Parsing/ParserState.php b/lib/Sabberworm/CSS/Parsing/ParserState.php
index ad79820a..2271d03e 100644
--- a/lib/Sabberworm/CSS/Parsing/ParserState.php
+++ b/lib/Sabberworm/CSS/Parsing/ParserState.php
@@ -48,8 +48,30 @@ public function getSettings() {
 		return $this->oParserSettings;
 	}
 
-	public function parseIdentifier($bIgnoreCase = true) {
-		$sResult = $this->parseCharacter(true);
+	public function parseIdentifier($bIgnoreCase = true, $bNameStartCodePoint = true) {
+        $sResult = null;
+        $bCanParseCharacter = true;
+
+        if ( $bNameStartCodePoint ) {
+            // Check if 3 code points would start an identifier. See <https://drafts.csswg.org/css-syntax-3/#would-start-an-identifier>.
+            $sNameStartCodePoint = '[a-zA-Z_]|[\x80-\xFF]';
+            $sEscapeCode = '\\[^\r\n\f]';
+
+            if (
+                ! (
+                    preg_match("/^-([-${sNameStartCodePoint}]|${sEscapeCode})/isSu", $this->peek(3)) ||
+                    preg_match("/^${sNameStartCodePoint}/isSu", $this->peek()) ||
+                    preg_match("/^${sEscapeCode}/isS", $this->peek(2))
+                )
+            ) {
+                $bCanParseCharacter = false;
+            }
+        }
+
+        if ( $bCanParseCharacter ) {
+            $sResult = $this->parseCharacter(true);
+        }
+
 		if ($sResult === null) {
 			throw new UnexpectedTokenException($sResult, $this->peek(5), 'identifier', $this->iLineNo);
 		}
@@ -97,13 +119,13 @@ public function parseCharacter($bIsForIdentifier) {
 		}
 		if ($bIsForIdentifier) {
 			$peek = ord($this->peek());
-			// Ranges: a-z A-Z 0-9 - _
+			// Matches a name code point. See <https://drafts.csswg.org/css-syntax-3/#name-code-point>.
 			if (($peek >= 97 && $peek <= 122) ||
 				($peek >= 65 && $peek <= 90) ||
 				($peek >= 48 && $peek <= 57) ||
 				($peek === 45) ||
 				($peek === 95) ||
-				($peek > 0xa1)) {
+				($peek > 0x81)) {
 				return $this->consume(1);
 			}
 		} else {
@@ -261,22 +283,22 @@ public function strlen($sString) {
 			return mb_strlen($sString, $this->sCharset);
 		} else {
 			return strlen($sString);
-		}	
-	}	
+		}
+	}
 
 	private function substr($iStart, $iLength) {
 		if ($iLength < 0) {
 			$iLength = $this->iLength - $iStart + $iLength;
-		}	
+		}
 		if ($iStart + $iLength > $this->iLength) {
 			$iLength = $this->iLength - $iStart;
-		}	
+		}
 		$sResult = '';
 		while ($iLength > 0) {
 			$sResult .= $this->aText[$iStart];
 			$iStart++;
 			$iLength--;
-		}	
+		}
 		return $sResult;
 	}
 
diff --git a/lib/Sabberworm/CSS/Value/Color.php b/lib/Sabberworm/CSS/Value/Color.php
index c6ed9b18..f02777f3 100644
--- a/lib/Sabberworm/CSS/Value/Color.php
+++ b/lib/Sabberworm/CSS/Value/Color.php
@@ -14,7 +14,7 @@ public static function parse(ParserState $oParserState) {
 		$aColor = array();
 		if ($oParserState->comes('#')) {
 			$oParserState->consume('#');
-			$sValue = $oParserState->parseIdentifier(false);
+			$sValue = $oParserState->parseIdentifier(false, false);
 			if ($oParserState->strlen($sValue) === 3) {
 				$sValue = $sValue[0] . $sValue[0] . $sValue[1] . $sValue[1] . $sValue[2] . $sValue[2];
 			} else if ($oParserState->strlen($sValue) === 4) {
diff --git a/tests/Sabberworm/CSS/ParserTest.php b/tests/Sabberworm/CSS/ParserTest.php
index ea34f2e7..ff8c5c92 100644
--- a/tests/Sabberworm/CSS/ParserTest.php
+++ b/tests/Sabberworm/CSS/ParserTest.php
@@ -214,7 +214,7 @@ function testManipulation() {
 		$this->assertSame('#header {margin: 10px 2em 1cm 2%;color: red !important;frequency: 30Hz;}
 body {color: green;}', $oDoc->render());
 	}
-	
+
 	function testRuleGetters() {
 		$oDoc = $this->parsedStructureForFile('values');
 		$aBlocks = $oDoc->getAllDeclarationBlocks();
@@ -319,7 +319,7 @@ function testNamespaces() {
 |test {gaga: 2;}';
 		$this->assertSame($sExpected, $oDoc->render());
 	}
-	
+
 	function testInnerColors() {
 		$oDoc = $this->parsedStructureForFile('inner-color');
 		$sExpected = 'test {background: -webkit-gradient(linear,0 0,0 bottom,from(#006cad),to(hsl(202,100%,49%)));}';
@@ -359,7 +359,7 @@ function testListValueRemoval() {
 		$this->assertSame('@media screen {html {some: -test(val2);}}
 #unrelated {other: yes;}', $oDoc->render());
 	}
-	
+
 	/**
 	* @expectedException Sabberworm\CSS\Parsing\OutputException
 	*/
@@ -766,4 +766,24 @@ function testLonelyImport() {
 		$sExpected = "@import url(\"example.css\") only screen and (max-width: 600px);";
 		$this->assertSame($sExpected, $oDoc->render());
 	}
+
+    function getInvalidIdentifiers() {
+        return array(
+            array('body { -0-transition: all .3s ease-in-out; }'),
+            array('body { 4-o-transition: all .3s ease-in-out; }'),
+        );
+	}
+
+    /**
+     * @dataProvider getInvalidIdentifiers
+     *
+     * @param string $css CSS text.
+     */
+    function testInvalidIdentifier($css) {
+        $this->setExpectedException( 'Sabberworm\CSS\Parsing\UnexpectedTokenException' );
+
+        $oSettings = Settings::create()->withLenientParsing(false);
+        $oParser = new Parser($css, $oSettings);
+        $oParser->parse();
+    }
 }