diff --git a/src/DiDom/Query.php b/src/DiDom/Query.php
index 85f2d1c..596d3ae 100644
--- a/src/DiDom/Query.php
+++ b/src/DiDom/Query.php
@@ -293,7 +293,7 @@ public static function buildXpath(array $segments, $prefix = '//')
 
         // if the pseudo class specified
         if (isset($segments['pseudo'])) {
-            $expression = isset($segments['expr']) ? trim($segments['expr']) : '';
+            $expression = isset($segments['pseudo-expression']) ? trim($segments['pseudo-expression']) : '';
 
             $parameters = explode(',', $expression);
             $parameters = array_map('trim', $parameters);
@@ -327,7 +327,7 @@ protected static function convertAttribute($name, $value)
 
         if ($isSimpleSelector) {
             // if specified only the attribute name
-            $xpath = $value === null ? '@'.$name : sprintf('@%s="%s"', $name, $value);
+            $xpath = $value === null ? '@' . $name : sprintf('@%s="%s"', $name, $value);
 
             return $xpath;
         }
@@ -458,85 +458,86 @@ public static function getSegments($selector)
         $selector = trim($selector);
 
         if ($selector === '') {
-            throw new InvalidSelectorException('The selector must not be empty');
+            throw new InvalidSelectorException('The selector must not be empty.');
         }
 
-        $tag = '(?P<tag>[\*|\w|\-]+)?';
-        $id = '(?:#(?P<id>[\w|\-]+))?';
-        $classes = '(?P<classes>\.[\w|\-|\.]+)*';
-        $attrs = '(?P<attrs>(?:\[.+?\])*)?';
-        $name = '(?P<pseudo>[\w\-]+)';
-        $expr = '(?:\((?P<expr>[^\)]+)\))';
-        $pseudo = '(?::'.$name.$expr.'?)?';
-        $rel = '\s*(?P<rel>>)?';
+        $pregMatchResult = preg_match(self::getSelectorRegex(), $selector, $segments);
 
-        $regexp = '/'.$tag.$id.$classes.$attrs.$pseudo.$rel.'/is';
-
-        if (preg_match($regexp, $selector, $segments)) {
-            if ($segments[0] === '') {
-                throw new InvalidSelectorException(sprintf('Invalid selector "%s"', $selector));
-            }
-
-            $result['selector'] = $segments[0];
+        if ($pregMatchResult === false || $pregMatchResult === 0 || $segments[0] === '') {
+            throw new InvalidSelectorException(sprintf('Invalid selector "%s".', $selector));
+        }
 
-            if (isset($segments['tag']) && $segments['tag'] !== '') {
-                $result['tag'] = $segments['tag'];
-            }
+        $result = ['selector' => $segments[0]];
 
-            // if the id attribute specified
-            if (isset($segments['id']) && $segments['id'] !== '') {
-                $result['id'] = $segments['id'];
-            }
+        if (isset($segments['tag']) && $segments['tag'] !== '') {
+            $result['tag'] = $segments['tag'];
+        }
 
-            // if the attributes specified
-            if (isset($segments['attrs'])) {
-                $attributes = trim($segments['attrs'], '[]');
-                $attributes = explode('][', $attributes);
+        // if the id attribute specified
+        if (isset($segments['id']) && $segments['id'] !== '') {
+            $result['id'] = $segments['id'];
+        }
 
-                foreach ($attributes as $attribute) {
-                    if ($attribute !== '') {
-                        list($name, $value) = array_pad(explode('=', $attribute, 2), 2, null);
+        // if the attributes specified
+        if (isset($segments['attrs'])) {
+            $attributes = trim($segments['attrs'], '[]');
+            $attributes = explode('][', $attributes);
 
-                        if ($name === '') {
-                            throw new InvalidSelectorException(sprintf('Invalid selector "%s": attribute name must not be empty', $selector));
-                        }
+            foreach ($attributes as $attribute) {
+                if ($attribute !== '') {
+                    list($name, $value) = array_pad(explode('=', $attribute, 2), 2, null);
 
-                        // equal null if specified only the attribute name
-                        $result['attributes'][$name] = is_string($value) ? trim($value, '\'"') : null;
+                    if ($name === '') {
+                        throw new InvalidSelectorException(sprintf('Invalid selector "%s": attribute name must not be empty', $selector));
                     }
-                }
-            }
-
-            // if the class attribute specified
-            if (isset($segments['classes'])) {
-                $classes = trim($segments['classes'], '.');
-                $classes = explode('.', $classes);
 
-                foreach ($classes as $class) {
-                    if ($class !== '') {
-                        $result['classes'][] = $class;
-                    }
+                    // equal null if specified only the attribute name
+                    $result['attributes'][$name] = is_string($value) ? trim($value, '\'"') : null;
                 }
             }
+        }
 
-            // if the pseudo class specified
-            if (isset($segments['pseudo']) && $segments['pseudo'] !== '') {
-                $result['pseudo'] = $segments['pseudo'];
+        // if the class attribute specified
+        if (isset($segments['classes'])) {
+            $classes = trim($segments['classes'], '.');
+            $classes = explode('.', $classes);
 
-                if (isset($segments['expr']) && $segments['expr'] !== '') {
-                    $result['expr'] = $segments['expr'];
+            foreach ($classes as $class) {
+                if ($class !== '') {
+                    $result['classes'][] = $class;
                 }
             }
+        }
 
-            // if it is a direct descendant
-            if (isset($segments['rel'])) {
-                $result['rel'] = $segments['rel'];
+        // if the pseudo class specified
+        if (isset($segments['pseudo']) && $segments['pseudo'] !== '') {
+            $result['pseudo'] = $segments['pseudo'];
+
+            if (isset($segments['pseudoExpr']) && $segments['pseudoExpr'] !== '') {
+                $result['pseudo-expression'] = $segments['pseudoExpr'];
             }
+        }
 
-            return $result;
+        // if it is a direct descendant
+        if (isset($segments['rel'])) {
+            $result['rel'] = $segments['rel'];
         }
 
-        throw new InvalidSelectorException(sprintf('Invalid selector "%s"', $selector));
+        return $result;
+    }
+
+    private static function getSelectorRegex()
+    {
+        $tag = '(?P<tag>[\*|\w|\-]+)?';
+        $id = '(?:#(?P<id>[\w|\-]+))?';
+        $classes = '(?P<classes>\.[\w|\-|\.]+)*';
+        $attrs = '(?P<attrs>(?:\[.+?\])*)?';
+        $pseudoType = '(?P<pseudo>[\w\-]+)';
+        $pseudoExpr = '(?:\((?P<pseudoExpr>[^\)]+)\))';
+        $pseudo = '(?::' . $pseudoType . $pseudoExpr . '?)?';
+        $rel = '\s*(?P<rel>>)?';
+
+        return '/' . $tag . $id . $classes . $attrs . $pseudo . $rel . '/is';
     }
 
     /**
diff --git a/tests/QueryTest.php b/tests/QueryTest.php
index b8da361..0b61e51 100644
--- a/tests/QueryTest.php
+++ b/tests/QueryTest.php
@@ -93,7 +93,7 @@ public function testCompileWithEmptyCssExpression()
 
     /**
      * @expectedException \DiDom\Exceptions\InvalidSelectorException
-     * @expectedExceptionMessage The selector must not be empty
+     * @expectedExceptionMessage The selector must not be empty.
      */
     public function testGetSegmentsWithEmptySelector()
     {
@@ -177,7 +177,7 @@ public function testUnknownNthExpression()
 
     /**
      * @expectedException \DiDom\Exceptions\InvalidSelectorException
-     * @expectedExceptionMessage Invalid selector "."
+     * @expectedExceptionMessage Invalid selector ".".
      */
     public function testGetSegmentsWithEmptyClassName()
     {
@@ -186,7 +186,7 @@ public function testGetSegmentsWithEmptyClassName()
 
     /**
      * @expectedException \DiDom\Exceptions\InvalidSelectorException
-     * @expectedExceptionMessage Invalid selector "."
+     * @expectedExceptionMessage Invalid selector ".".
      */
     public function testCompilehWithEmptyClassName()
     {
@@ -239,7 +239,8 @@ public function compileCssTests()
             ['foo bar baz', '//foo//bar//baz'],
             ['foo > bar > baz', '//foo/bar/baz'],
             ['#foo', '//*[@id="foo"]'],
-            ['.bar', '//*[contains(concat(" ", normalize-space(@class), " "), " bar ")]'],
+            ['.foo', '//*[contains(concat(" ", normalize-space(@class), " "), " foo ")]'],
+            ['.foo.bar', '//*[(contains(concat(" ", normalize-space(@class), " "), " foo ")) and (contains(concat(" ", normalize-space(@class), " "), " bar "))]'],
             ['*[foo=bar]', '//*[@foo="bar"]'],
             ['*[foo="bar"]', '//*[@foo="bar"]'],
             ['*[foo=\'bar\']', '//*[@foo="bar"]'],
@@ -418,7 +419,7 @@ public function getSegmentsTests()
             ['selector' => 'li:first-child', 'tag' => 'li', 'pseudo' => 'first-child'],
             ['selector' => 'ul >', 'tag' => 'ul', 'rel' => '>'],
             ['selector' => '#id.foo[name=value]:first-child >', 'id' => 'id', 'classes' => ['foo'], 'attributes' => ['name' => 'value'], 'pseudo' => 'first-child', 'rel' => '>'],
-            ['selector' => 'li.bar:nth-child(2n)', 'tag' => 'li', 'classes' => ['bar'], 'pseudo' => 'nth-child', 'expr' => '2n'],
+            ['selector' => 'li.bar:nth-child(2n)', 'tag' => 'li', 'classes' => ['bar'], 'pseudo' => 'nth-child', 'pseudo-expression' => '2n'],
         ];
 
         $parameters = [];