diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index f2c2c0324c..f81ca93bad 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -68,6 +68,7 @@ Yii Framework 2 Change Log
 - Enh #12382: Changed `yii\widgets\MaskedInput` to use `jQuery` instead of `$` to prevent conflicts (samdark)
 - Bug #12446: Disable slaves when execute migrations to resolve master-slave replication no-sync (lichunqiang)
 - Bug #12423: Fixed migration tool problem of creating fields with brackets in comment (pana1990)
+- Bug #12537: Fixes issues with spaces in `StringHelper:truncateHtml` (Alex-Code)
 
 2.0.9 July 11, 2016
 -------------------
diff --git a/framework/helpers/BaseStringHelper.php b/framework/helpers/BaseStringHelper.php
index d5aaf37334..77c46b71fb 100644
--- a/framework/helpers/BaseStringHelper.php
+++ b/framework/helpers/BaseStringHelper.php
@@ -109,7 +109,7 @@ class BaseStringHelper
         }
         
         if (mb_strlen($string, $encoding ?: Yii::$app->charset) > $length) {
-            return trim(mb_substr($string, 0, $length, $encoding ?: Yii::$app->charset)) . $suffix;
+            return rtrim(mb_substr($string, 0, $length, $encoding ?: Yii::$app->charset)) . $suffix;
         } else {
             return $string;
         }
@@ -164,16 +164,14 @@ class BaseStringHelper
                 $truncated[] = $token;
             } elseif ($token instanceof \HTMLPurifier_Token_Text && $totalCount <= $count) { //Text
                 if (false === $encoding) {
-                    $token->data = self::truncateWords($token->data, $count - $totalCount, '');
+                    preg_match('/^(\s*)/um', $token->data, $prefixSpace) ?: $prefixSpace = ['',''];
+                    $token->data = $prefixSpace[1] . self::truncateWords(ltrim($token->data), $count - $totalCount, '');
                     $currentCount = self::countWords($token->data);
                 } else {
-                    $token->data = self::truncate($token->data, $count - $totalCount, '', $encoding) . ' ';
+                    $token->data = self::truncate($token->data, $count - $totalCount, '', $encoding);
                     $currentCount = mb_strlen($token->data, $encoding);
                 }
                 $totalCount += $currentCount;
-                if (1 === $currentCount) {
-                    $token->data = ' ' . $token->data;
-                }
                 $truncated[] = $token;
             } elseif ($token instanceof \HTMLPurifier_Token_End) { //Tag ends
                 $openTokens--;
diff --git a/tests/framework/helpers/StringHelperTest.php b/tests/framework/helpers/StringHelperTest.php
index 318e8db7f9..cb210a538d 100644
--- a/tests/framework/helpers/StringHelperTest.php
+++ b/tests/framework/helpers/StringHelperTest.php
@@ -107,8 +107,14 @@ class StringHelperTest extends TestCase
         $this->assertEquals('исполь!!!', StringHelper::truncate('используем восклицательные знаки', 6, '!!!'));
 
         // With Html
-        $this->assertEquals('<span>This is a test </span>...', StringHelper::truncate('<span>This is a test sentance</span>', 14, '...', null, true));
-        $this->assertEquals('<span><img src="image.png" />This is a test </span>...', StringHelper::truncate('<span><img src="image.png" />This is a test sentance</span>', 14, '...', null, true));
+        $this->assertEquals('<span>This is a test</span>...', StringHelper::truncate('<span>This is a test sentance</span>', 14, '...', null, true));
+        $this->assertEquals('<span>This is a test</span>...', StringHelper::truncate('<span>This is a test </span>sentance', 14, '...', null, true));
+        $this->assertEquals('<span>This is a test </span><strong>for</strong>...', StringHelper::truncate('<span>This is a test </span><strong>for a sentance</strong>', 18, '...', null, true));
+        $this->assertEquals('<span>This is a test</span><strong> for</strong>...', StringHelper::truncate('<span>This is a test</span><strong> for a sentance</strong>', 18, '...', null, true));
+        
+        $this->assertEquals('<span><img src="image.png" />This is a test</span>...', StringHelper::truncate('<span><img src="image.png" />This is a test sentance</span>', 14, '...', null, true));
+        $this->assertEquals('<span><img src="image.png" />This is a test</span>...', StringHelper::truncate('<span><img src="image.png" />This is a test </span>sentance', 14, '...', null, true));
+        $this->assertEquals('<span><img src="image.png" />This is a test </span><strong>for</strong>...', StringHelper::truncate('<span><img src="image.png" />This is a test </span><strong>for a sentance</strong>', 18, '...', null, true));
     }
 
     public function testTruncateWords()
@@ -119,10 +125,16 @@ class StringHelperTest extends TestCase
         $this->assertEquals('это строка с          неожиданными...', StringHelper::truncateWords('это строка с          неожиданными пробелами', 4));
 
         $this->assertEquals('lorem ipsum', StringHelper::truncateWords('lorem ipsum', 3, '...', true));
+        $this->assertEquals(' lorem ipsum', StringHelper::truncateWords(' lorem ipsum', 3, '...', true));
         // With Html
         $this->assertEquals('<span>This is a test</span>...', StringHelper::truncateWords('<span>This is a test sentance</span>', 4, '...', true));
-        $this->assertEquals('<span><img src="image.png" />This is a test</span>...', StringHelper::truncateWords('<span><img src="image.png" />This is a test sentance</span>', 4, '...', true));
+        $this->assertEquals('<span>This is a test </span><strong>for</strong>...', StringHelper::truncateWords('<span>This is a test </span><strong>for a sentance</strong>', 5, '...', true));
+        $this->assertEquals('<span>This is a test</span><strong> for</strong>...', StringHelper::truncateWords('<span>This is a test</span><strong> for a sentance</strong>', 5, '...', true));
         $this->assertEquals('<p> раз два три четыре пять </p> <p> шесть</p>...', StringHelper::truncateWords('<p> раз два три четыре пять </p> <p> шесть семь восемь девять десять</p>', 6, '...', true));
+
+        $this->assertEquals('<span><img src="image.png" />This is a test</span>...', StringHelper::truncateWords('<span><img src="image.png" />This is a test sentance</span>', 4, '...', true));
+        $this->assertEquals('<span><img src="image.png" />This is a test </span><strong>for</strong>...', StringHelper::truncateWords('<span><img src="image.png" />This is a test </span><strong>for a sentance</strong>', 5, '...', true));
+        $this->assertEquals('<span><img src="image.png" />This is a test</span><strong> for</strong>...', StringHelper::truncateWords('<span><img src="image.png" />This is a test</span><strong> for a sentance</strong>', 5, '...', true));        
     }
 
     /**