diff -u b/core/modules/breakpoint/lib/Drupal/breakpoint/Breakpoint.php b/core/modules/breakpoint/lib/Drupal/breakpoint/Breakpoint.php
--- b/core/modules/breakpoint/lib/Drupal/breakpoint/Breakpoint.php
+++ b/core/modules/breakpoint/lib/Drupal/breakpoint/Breakpoint.php
@@ -295,7 +295,7 @@
         foreach ($query_parts as $query_part) {
           $matches = array();
           // Check expression: '(' S* media_feature S* [ ':' S* expr ]? ')' S*
-          if (preg_match('/^\(([\w\-]+)(:\s?([\w\-]+))?\)/', trim($query_part), $matches)) {
+          if (preg_match('/^\(([\w\-]+)(:\s?([\w\-\.]+))?\)/', trim($query_part), $matches)) {
             // Single expression.
             if (isset($matches[1]) && !isset($matches[2])) {
               if (!array_key_exists($matches[1], $media_features)) {
@@ -318,7 +318,7 @@
                 switch ($media_features[$matches[1]]) {
                   case 'length':
                     $length_matches = array();
-                    if (preg_match('/^(\-)?(\d+)?((?:|em|ex|px|cm|mm|in|pt|pc|deg|rad|grad|ms|s|hz|khz|dpi|dpcm))$/i', trim($value), $length_matches)) {
+                    if (preg_match('/^(\-)?(\d+(?:\.\d+)?)?((?:|em|ex|px|cm|mm|in|pt|pc|deg|rad|grad|ms|s|hz|khz|dpi|dpcm))$/i', trim($value), $length_matches)) {
                       // Only -0 is allowed.
                       if ($length_matches[1] === '-' && $length_matches[2] !== '0') {
                         throw new InvalidBreakpointMediaQueryException('Invalid length detected.');
diff -u b/core/modules/breakpoint/lib/Drupal/breakpoint/Tests/BreakpointMediaQueryTest.php b/core/modules/breakpoint/lib/Drupal/breakpoint/Tests/BreakpointMediaQueryTest.php
--- b/core/modules/breakpoint/lib/Drupal/breakpoint/Tests/BreakpointMediaQueryTest.php
+++ b/core/modules/breakpoint/lib/Drupal/breakpoint/Tests/BreakpointMediaQueryTest.php
@@ -52,6 +52,7 @@
       'screen and (width: 0em)',
       'screen and (min-width: -0)',
       'screen and (max-width: 0)',
+      'screen and (max-width: 0.3)',
       'screen and (min-width)',
       // Multiline and comments.
       'screen and /* this is a comment */ (min-width)',
@@ -60,12 +61,7 @@
     );
 
     foreach ($media_queries as $media_query) {
-      try {
-        $this->assertTrue(Breakpoint::isValidMediaQuery($media_query), $media_query . ' is valid.');
-      }
-      catch (InvalidBreakpointMediaQueryException $e) {
-        $this->assertTrue(FALSE, $media_query . ' is valid.');
-      }
+      $this->assertTrue(Breakpoint::isValidMediaQuery($media_query), $media_query . ' is valid.');
     }
   }