diff --git a/library/HTMLPurifier/AttrDef/CSS/Number.php b/library/HTMLPurifier/AttrDef/CSS/Number.php
index 8edc159e..ef49d20f 100644
--- a/library/HTMLPurifier/AttrDef/CSS/Number.php
+++ b/library/HTMLPurifier/AttrDef/CSS/Number.php
@@ -69,7 +69,13 @@ class HTMLPurifier_AttrDef_CSS_Number extends HTMLPurifier_AttrDef
             return false;
         }
 
-        $left = ltrim($left, '0');
+        // Remove leading zeros until positive number or a zero stays left
+        if (ltrim($left, '0') != '') {
+            $left = ltrim($left, '0');
+        } else {
+            $left = '0';
+        }
+
         $right = rtrim($right, '0');
 
         if ($right === '') {
diff --git a/tests/HTMLPurifier/AttrDef/CSS/AlphaValueTest.php b/tests/HTMLPurifier/AttrDef/CSS/AlphaValueTest.php
index b360f844..34929f18 100644
--- a/tests/HTMLPurifier/AttrDef/CSS/AlphaValueTest.php
+++ b/tests/HTMLPurifier/AttrDef/CSS/AlphaValueTest.php
@@ -9,7 +9,7 @@ class HTMLPurifier_AttrDef_CSS_AlphaValueTest extends HTMLPurifier_AttrDefHarnes
 
         $this->assertDef('0');
         $this->assertDef('1');
-        $this->assertDef('.2');
+        $this->assertDef('0.2');
 
         // clamping to [0.0, 1,0]
         $this->assertDef('1.2', '1');
diff --git a/tests/HTMLPurifier/AttrDef/CSS/BackgroundTest.php b/tests/HTMLPurifier/AttrDef/CSS/BackgroundTest.php
index 8d826f87..5faff98c 100644
--- a/tests/HTMLPurifier/AttrDef/CSS/BackgroundTest.php
+++ b/tests/HTMLPurifier/AttrDef/CSS/BackgroundTest.php
@@ -17,7 +17,7 @@ class HTMLPurifier_AttrDef_CSS_BackgroundTest extends HTMLPurifier_AttrDefHarnes
         );
         $this->assertDef(
             'rgba(74, 12, 85, 0.35) repeat fixed bottom',
-            'rgba(74,12,85,.35) repeat fixed bottom'
+            'rgba(74,12,85,0.35) repeat fixed bottom'
         );
         $this->assertDef(
             'hsl(244, 47.4%, 88.1%) right center',
diff --git a/tests/HTMLPurifier/AttrDef/CSS/ColorTest.php b/tests/HTMLPurifier/AttrDef/CSS/ColorTest.php
index 74a6692e..bab74d03 100644
--- a/tests/HTMLPurifier/AttrDef/CSS/ColorTest.php
+++ b/tests/HTMLPurifier/AttrDef/CSS/ColorTest.php
@@ -20,8 +20,8 @@ class HTMLPurifier_AttrDef_CSS_ColorTest extends HTMLPurifier_AttrDefHarness
         $this->assertDef('rgb(12%,150%,0%)', 'rgb(12%,100%,0%)'); // percentage max values
 
         $this->assertDef('rgba(255, 0, 0, 0)', 'rgba(255,0,0,0)'); // rm spaces
-        $this->assertDef('rgba(100%,0%,0%,.4)');
-        $this->assertDef('rgba(38.1%,59.7%,1.8%,0.7)', 'rgba(38.1%,59.7%,1.8%,.7)'); // decimals okay
+        $this->assertDef('rgba(100%,0%,0%,0.4)');
+        $this->assertDef('rgba(38.1%,59.7%,1.8%,0.7)', 'rgba(38.1%,59.7%,1.8%,0.7)'); // decimals okay
 
         $this->assertDef('hsl(275, 45%, 81%)', 'hsl(275,45%,81%)'); // rm spaces
         $this->assertDef('hsl(100,0%,0%)');
@@ -30,8 +30,8 @@ class HTMLPurifier_AttrDef_CSS_ColorTest extends HTMLPurifier_AttrDefHarness
         $this->assertDef('hsl(380,125%,0%)', 'hsl(360,100%,0%)'); // max values
 
         $this->assertDef('hsla(100, 74%, 29%, 0)', 'hsla(100,74%,29%,0)'); // rm spaces
-        $this->assertDef('hsla(154,87%,21%,.4)');
-        $this->assertDef('hsla(45,94.3%,4.1%,0.7)', 'hsla(45,94.3%,4.1%,.7)'); // decimals okay
+        $this->assertDef('hsla(154,87%,21%,0.4)');
+        $this->assertDef('hsla(45,94.3%,4.1%,0.7)', 'hsla(45,94.3%,4.1%,0.7)'); // decimals okay
 
         $this->assertDef('#G00', false);
         $this->assertDef('cmyk(40, 23, 43, 23)', false);
diff --git a/tests/HTMLPurifier/AttrDef/CSS/NumberTest.php b/tests/HTMLPurifier/AttrDef/CSS/NumberTest.php
index 943bf5c0..6e9d44d4 100644
--- a/tests/HTMLPurifier/AttrDef/CSS/NumberTest.php
+++ b/tests/HTMLPurifier/AttrDef/CSS/NumberTest.php
@@ -12,8 +12,8 @@ class HTMLPurifier_AttrDef_CSS_NumberTest extends HTMLPurifier_AttrDefHarness
         $this->assertDef('1.0', '1');
         $this->assertDef('34');
         $this->assertDef('4.5');
-        $this->assertDef('.5');
-        $this->assertDef('0.5', '.5');
+        $this->assertDef('0.5');
+        $this->assertDef('0.5', '0.5');
         $this->assertDef('-56.9');
 
         $this->assertDef('0.', '0');
@@ -21,10 +21,10 @@ class HTMLPurifier_AttrDef_CSS_NumberTest extends HTMLPurifier_AttrDefHarness
         $this->assertDef('0.0', '0');
 
         $this->assertDef('1.', '1');
-        $this->assertDef('.1', '.1');
+        $this->assertDef('.1', '0.1');
 
         $this->assertDef('1.0', '1');
-        $this->assertDef('0.1', '.1');
+        $this->assertDef('0.1', '0.1');
 
         $this->assertDef('000', '0');
         $this->assertDef(' 9', '9');
diff --git a/tests/HTMLPurifier/AttrDef/CSSTest.php b/tests/HTMLPurifier/AttrDef/CSSTest.php
index 7ad5788e..318f471f 100644
--- a/tests/HTMLPurifier/AttrDef/CSSTest.php
+++ b/tests/HTMLPurifier/AttrDef/CSSTest.php
@@ -140,8 +140,8 @@ class HTMLPurifier_AttrDef_CSSTest extends HTMLPurifier_AttrDefHarness
         $this->assertDef('scrollbar-highlight-color:#ff69b4;');
         $this->assertDef('scrollbar-shadow-color:#f0f;');
 
-        $this->assertDef('-moz-opacity:.2;');
-        $this->assertDef('-khtml-opacity:.2;');
+        $this->assertDef('-moz-opacity:0.2;');
+        $this->assertDef('-khtml-opacity:0.2;');
         $this->assertDef('filter:alpha(opacity=20);');
 
         $this->assertDef('border-top-left-radius:55pt 25pt;');
@@ -160,7 +160,7 @@ class HTMLPurifier_AttrDef_CSSTest extends HTMLPurifier_AttrDefHarness
         $this->assertDef('display:none;');
         $this->assertDef('visibility:visible;');
         $this->assertDef('overflow:scroll;');
-        $this->assertDef('opacity:.2;');
+        $this->assertDef('opacity:0.2;');
     }
 
     public function testForbidden()