diff --git a/src/Support/MutationGenerator.php b/src/Support/MutationGenerator.php
index d712121..7fb47a4 100644
--- a/src/Support/MutationGenerator.php
+++ b/src/Support/MutationGenerator.php
@@ -154,7 +154,7 @@ private function doesNotContainClassToMutate(string $contents, array $classesToM
             $namespace = preg_quote(implode('\\', $parts));
             $classOrNamespace = preg_quote($classOrNamespace);
 
-            if (preg_match("/namespace\\s+$namespace/", $contents) === 1 && preg_match("/(?:class|trait)\\s+$class.*/", $contents) === 1) {
+            if (preg_match("/namespace\\s+$namespace/", $contents) === 1 && preg_match("/(?:class|trait)\\s+$class\b.*/", $contents) === 1) {
                 return false;
             }
 
diff --git a/tests/Unit/MutationGeneratorTest.php b/tests/Unit/MutationGeneratorTest.php
index 79c67ed..00163f9 100644
--- a/tests/Unit/MutationGeneratorTest.php
+++ b/tests/Unit/MutationGeneratorTest.php
@@ -96,7 +96,7 @@ classesToMutate: $classes,
     [['AgeHelper'], 2],
     [['SizeHelper'], 0],
     [[AgeHelper::class], 2],
-    [['Tests\\Fixtures\\Classes\\AgeHelp'], 2],
+    [['Tests\\Fixtures\\Classes\\AgeHelp'], 0],
     [['Invalid\\Namespace\\AgeHelper'], 0],
     [['Invalid\\Namespace\\AgeHelp'], 0],
     [['Invalid\\Namespace\\AgeHelper', AgeHelper::class], 2],
@@ -118,7 +118,7 @@ classesToMutate: $classes,
     [[SizeHelper::class], 0],
     [[SizeHelperTrait::class, SizeHelper::class], 1],
     [['SizeHelperTrait'], 1],
-    [['Tests\\Fixtures\\Traits\\SizeHelperTrai'], 1],
+    [['Tests\\Fixtures\\Traits\\SizeHelperTrai'], 0],
     [['Invalid\\Namespace\\SizeHelperTrait'], 0],
 ]);