diff --git a/src/Prefixer.php b/src/Prefixer.php
index 06877b24..90c6007e 100644
--- a/src/Prefixer.php
+++ b/src/Prefixer.php
@@ -217,7 +217,7 @@ public function replaceClassname($contents, $originalClassname, $classnamePrefix
 								    		        	# the remainder of the string.
                 namespace\s+[a-zA-Z0-9_\x7f-\xff\\\\]+; # Skip lines just declaring the namespace.
                 |		        	
-				([^a-zA-Z0-9_\x7f-\xff\$])('. $searchClassname . ')([^a-zA-Z0-9_\x7f-\xff])
+				([^a-zA-Z0-9_\x7f-\xff\$\\\])('. $searchClassname . ')([^a-zA-Z0-9_\x7f-\xff\\\])
 				
 			/x'; //                                     # x: ignore whitespace in regex.
 
diff --git a/tests/Unit/PrefixerTest.php b/tests/Unit/PrefixerTest.php
index 9d183d63..22a9b6d8 100644
--- a/tests/Unit/PrefixerTest.php
+++ b/tests/Unit/PrefixerTest.php
@@ -1317,4 +1317,74 @@ class NA
 
         $this->assertEquals($contents, $result);
     }
+
+    /**
+     * class Normalizer_Test_Normalizer extends Normalizer_Test\Symfony\Polyfill\Intl\Normalizer_Test_Normalizer\Normalizer
+     *
+     * @throws \Exception
+     */
+    public function testItDoesNotPrefixClassnameInsideInsideNamespaceName(): void
+    {
+
+        $contents = <<<'EOD'
+class Normalizer extends Symfony\Polyfill\Intl\Normalizer\Foo
+{
+
+}
+EOD;
+
+        $expected = <<<'EOD'
+class Normalizer_Test_Normalizer extends Symfony\Polyfill\Intl\Normalizer\Foo
+{
+
+}
+EOD;
+
+        $originalClassname = 'Normalizer';
+        $classnamePrefix = 'Normalizer_Test_';
+
+        $config = $this->createMock(StraussConfig::class);
+
+        $replacer = new Prefixer($config, __DIR__);
+
+        $result = $replacer->replaceClassname($contents, $originalClassname, $classnamePrefix);
+
+        $this->assertEquals($expected, $result);
+    }
+
+
+
+    /**
+     * class Normalizer_Test_Normalizer extends Normalizer_Test\Symfony\Polyfill\Intl\Normalizer_Test_Normalizer\Normalizer
+     *
+     * @throws \Exception
+     */
+    public function testItDoesNotPrefixClassnameInsideEndNamespaceName(): void
+    {
+
+        $contents = <<<'EOD'
+class Normalizer extends Symfony\Polyfill\Intl\Foo\Normalizer
+{
+
+}
+EOD;
+
+        $expected = <<<'EOD'
+class Normalizer_Test_Normalizer extends Symfony\Polyfill\Intl\Foo\Normalizer
+{
+
+}
+EOD;
+
+        $originalClassname = 'Normalizer';
+        $classnamePrefix = 'Normalizer_Test_';
+
+        $config = $this->createMock(StraussConfig::class);
+
+        $replacer = new Prefixer($config, __DIR__);
+
+        $result = $replacer->replaceClassname($contents, $originalClassname, $classnamePrefix);
+
+        $this->assertEquals($expected, $result);
+    }
 }