diff --git a/src/Parsing/ParserState.php b/src/Parsing/ParserState.php
index 2427c5e1..099dab13 100644
--- a/src/Parsing/ParserState.php
+++ b/src/Parsing/ParserState.php
@@ -142,12 +142,36 @@ public function setPosition($iPosition)
      *
      * @throws UnexpectedTokenException
      */
-    public function parseIdentifier($bIgnoreCase = true)
+    public function parseIdentifier($bIgnoreCase = true, $bNameStartCodePoint = true)
     {
         if ($this->isEnd()) {
             throw new UnexpectedEOFException('', '', 'identifier', $this->iLineNo);
         }
-        $sResult = $this->parseCharacter(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', $this->iLineNo);
         }
@@ -211,14 +235,15 @@ public function parseCharacter($bIsForIdentifier)
         }
         if ($bIsForIdentifier) {
             $peek = ord($this->peek());
-            // Ranges: a-z A-Z 0-9 - _
+            $peek = ord($this->peek());
+            // 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 >= 97 && $peek <= 122) ||
+                ($peek >= 65 && $peek <= 90) ||
+                ($peek >= 48 && $peek <= 57) ||
+                ($peek === 45) ||
+                ($peek === 95) ||
+                ($peek > 0x81)
             ) {
                 return $this->consume(1);
             }
diff --git a/src/Value/Color.php b/src/Value/Color.php
index a002760b..26180c62 100644
--- a/src/Value/Color.php
+++ b/src/Value/Color.php
@@ -36,7 +36,7 @@ public static function parse(ParserState $oParserState, $bIgnoreCase = false)
         $aColor = [];
         if ($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] . $sValue[2];
             } elseif ($oParserState->strlen($sValue) === 4) {
diff --git a/tests/ParserTest.php b/tests/ParserTest.php
index c8e8ac76..1ec634f7 100644
--- a/tests/ParserTest.php
+++ b/tests/ParserTest.php
@@ -1261,6 +1261,29 @@ public function lonelyImport()
         self::assertSame($sExpected, $oDoc->render());
     }
 
+    public function getInvalidIdentifiers()
+    {
+        return [
+            ['body { -0-transition: all .3s ease-in-out; }'],
+            ['body { 4-o-transition: all .3s ease-in-out; }'],
+        ];
+    }
+
+    /**
+     * @dataProvider getInvalidIdentifiers
+     *
+     * @param string $css CSS text.
+     * @test
+     */
+    public function invalidIdentifier($css)
+    {
+        $this->expectException(\Sabberworm\CSS\Parsing\UnexpectedTokenException::class);
+
+        $oSettings = Settings::create()->withLenientParsing(false);
+        $oParser   = new Parser($css, $oSettings);
+        $oParser->parse();
+    }
+
     public function escapedSpecialCaseTokens()
     {
         $oDoc = $this->parsedStructureForFile('escaped-tokens');