diff --git a/src/HJSON/HJSONParser.php b/src/HJSON/HJSONParser.php
index 1ba5e06..b6c110d 100644
--- a/src/HJSON/HJSONParser.php
+++ b/src/HJSON/HJSONParser.php
@@ -368,9 +368,8 @@ private function peek($offs)
     {
         $index = $this->at + $offs;
 
-        // Mimic old behavior with mb_substr
         if ($index < 0) {
-            $index = 0;
+            return null;
         }
         if ($index >= $this->textLengthChars) {
             return "";
diff --git a/tests/assets/failStr9a_test.hjson b/tests/assets/failStr9a_test.hjson
new file mode 100644
index 0000000..229b94d
--- /dev/null
+++ b/tests/assets/failStr9a_test.hjson
@@ -0,0 +1,4 @@
+[
+[
+=
+[[''''''
diff --git a/tests/assets/strings3_result.hjson b/tests/assets/strings3_result.hjson
new file mode 100644
index 0000000..e16c76d
--- /dev/null
+++ b/tests/assets/strings3_result.hjson
@@ -0,0 +1 @@
+""
diff --git a/tests/assets/strings3_result.json b/tests/assets/strings3_result.json
new file mode 100644
index 0000000..e16c76d
--- /dev/null
+++ b/tests/assets/strings3_result.json
@@ -0,0 +1 @@
+""
diff --git a/tests/assets/strings3_test.hjson b/tests/assets/strings3_test.hjson
new file mode 100644
index 0000000..9cad736
--- /dev/null
+++ b/tests/assets/strings3_test.hjson
@@ -0,0 +1 @@
+''''''