diff --git a/library/HTMLPurifier/AttrDef/CSS/Background.php b/library/HTMLPurifier/AttrDef/CSS/Background.php
index 7f1ea3b0..28c49883 100644
--- a/library/HTMLPurifier/AttrDef/CSS/Background.php
+++ b/library/HTMLPurifier/AttrDef/CSS/Background.php
@@ -25,6 +25,7 @@ class HTMLPurifier_AttrDef_CSS_Background extends HTMLPurifier_AttrDef
         $this->info['background-repeat'] = $def->info['background-repeat'];
         $this->info['background-attachment'] = $def->info['background-attachment'];
         $this->info['background-position'] = $def->info['background-position'];
+        $this->info['background-size'] = $def->info['background-size'];
     }
 
     /**
@@ -53,6 +54,7 @@ class HTMLPurifier_AttrDef_CSS_Background extends HTMLPurifier_AttrDef
         $caught['repeat'] = false;
         $caught['attachment'] = false;
         $caught['position'] = false;
+        $caught['size'] = false;
 
         $i = 0; // number of catches
 
diff --git a/library/HTMLPurifier/CSSDefinition.php b/library/HTMLPurifier/CSSDefinition.php
index 21f1a589..3f08b81c 100644
--- a/library/HTMLPurifier/CSSDefinition.php
+++ b/library/HTMLPurifier/CSSDefinition.php
@@ -109,6 +109,22 @@ class HTMLPurifier_CSSDefinition extends HTMLPurifier_Definition
         );
         $this->info['background-position'] = new HTMLPurifier_AttrDef_CSS_BackgroundPosition();
 
+        $this->info['background-size'] = new HTMLPurifier_AttrDef_CSS_Composite(
+            array(
+                new HTMLPurifier_AttrDef_Enum(
+                    array(
+                        'auto',
+                        'cover',
+                        'contain',
+                        'initial',
+                        'inherit',
+                    )
+                ),
+                new HTMLPurifier_AttrDef_CSS_Percentage(),
+                new HTMLPurifier_AttrDef_CSS_Length()
+            )
+        );
+
         $border_color =
             $this->info['border-top-color'] =
             $this->info['border-bottom-color'] =
diff --git a/tests/HTMLPurifier/AttrDef/CSSTest.php b/tests/HTMLPurifier/AttrDef/CSSTest.php
index 318f471f..17a56581 100644
--- a/tests/HTMLPurifier/AttrDef/CSSTest.php
+++ b/tests/HTMLPurifier/AttrDef/CSSTest.php
@@ -92,6 +92,9 @@ class HTMLPurifier_AttrDef_CSSTest extends HTMLPurifier_AttrDefHarness
         $this->assertDef('background-repeat:repeat-y;');
         $this->assertDef('background-attachment:fixed;');
         $this->assertDef('background-position:left 90%;');
+        $this->assertDef('background-size:50%;');
+        $this->assertDef('background-size:cover;');
+        $this->assertDef('background-size:200px;');
         $this->assertDef('border-spacing:1em;');
         $this->assertDef('border-spacing:1em 2em;');
         $this->assertDef('border-color: rgb(0, 0, 0) rgb(10,0,10)', 'border-color:rgb(0,0,0) rgb(10,0,10);');