diff --git a/index.php b/index.php
index 6a458797..6e67e855 100644
--- a/index.php
+++ b/index.php
@@ -448,7 +448,10 @@ public function createBackup(): void {
 		}
 
 		foreach ($this->getRecursiveDirectoryIterator($this->nextcloudDir, $excludedElements) as $absolutePath => $fileInfo) {
-			$relativePath = explode($this->nextcloudDir, $absolutePath)[1];
+			$relativePath = explode($this->nextcloudDir, $absolutePath, 2)[1] ?? null;
+			if ($relativePath === null) {
+				throw new \Exception($absolutePath . ' is not in ' . $this->nextcloudDir);
+			}
 			$relativeDirectory = dirname($relativePath);
 
 			// Create folder if it doesn't exist
diff --git a/lib/Updater.php b/lib/Updater.php
index d3927a05..b4799183 100644
--- a/lib/Updater.php
+++ b/lib/Updater.php
@@ -431,7 +431,10 @@ public function createBackup(): void {
 		}
 
 		foreach ($this->getRecursiveDirectoryIterator($this->nextcloudDir, $excludedElements) as $absolutePath => $fileInfo) {
-			$relativePath = explode($this->nextcloudDir, $absolutePath)[1];
+			$relativePath = explode($this->nextcloudDir, $absolutePath, 2)[1] ?? null;
+			if ($relativePath === null) {
+				throw new \Exception($absolutePath . ' is not in ' . $this->nextcloudDir);
+			}
 			$relativeDirectory = dirname($relativePath);
 
 			// Create folder if it doesn't exist
diff --git a/tests/checkSameCodeBase.php b/tests/checkSameCodeBase.php
index 400a11c5..969747e7 100644
--- a/tests/checkSameCodeBase.php
+++ b/tests/checkSameCodeBase.php
@@ -55,7 +55,7 @@ function findDiffPos($original, $copy) {
  * @var SplFileInfo $fileInfo
  */
 foreach ($iterator as $path => $fileInfo) {
-	$fileName = explode($libDir, $path)[1];
+	$fileName = explode($libDir, $path, 2)[1];
 
 	if (array_search($fileName, $excludedFiles) !== false) {
 		continue;