diff --git a/src/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocator.php b/src/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocator.php
index 72c7e08e8a..26c35c557d 100644
--- a/src/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocator.php
+++ b/src/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocator.php
@@ -229,7 +229,10 @@ private function findSymbols(string $file): array
 					$functions[] = $namespacedName;
 				} else {
 					if ($matches['type'][$i] === 'enum') {
-						$namespacedName = rtrim($namespacedName, ':');
+						$colonPos = strrpos($namespacedName, ':');
+						if (false !== $colonPos) {
+							$namespacedName = substr($namespacedName, 0, $colonPos);
+						}
 					}
 					$classes[] = $namespacedName;
 				}
diff --git a/tests/PHPStan/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocatorTest.php b/tests/PHPStan/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocatorTest.php
index 736d9b6837..a447c1b851 100644
--- a/tests/PHPStan/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocatorTest.php
+++ b/tests/PHPStan/Reflection/BetterReflection/SourceLocator/OptimizedDirectorySourceLocatorTest.php
@@ -47,6 +47,12 @@ public function dataClass(): iterable
 			'OptimizedDirectory\\TestEnum',
 			'enum.php',
 		];
+
+		yield [
+			'OptimizedDirectory\\BackedByStringWithoutSpace',
+			'OptimizedDirectory\\BackedByStringWithoutSpace',
+			'enum.php',
+		];
 	}
 
 	/**
diff --git a/tests/PHPStan/Reflection/BetterReflection/SourceLocator/data/directory/enum.php b/tests/PHPStan/Reflection/BetterReflection/SourceLocator/data/directory/enum.php
index 1f9996f4f7..4d1a990dc5 100644
--- a/tests/PHPStan/Reflection/BetterReflection/SourceLocator/data/directory/enum.php
+++ b/tests/PHPStan/Reflection/BetterReflection/SourceLocator/data/directory/enum.php
@@ -8,3 +8,8 @@ enum TestEnum: int
 	case ONE = 1;
 
 }
+
+enum BackedByStringWithoutSpace:string
+{
+	// cases
+}