diff --git a/phpseclib/Math/BigInteger.php b/phpseclib/Math/BigInteger.php
index 36e6ce99..0f60b8a9 100644
--- a/phpseclib/Math/BigInteger.php
+++ b/phpseclib/Math/BigInteger.php
@@ -445,7 +445,7 @@ class BigInteger
                 // (?<=^|-)0*: find any 0's that are preceded by the start of the string or by a - (ie. octals)
                 // [^-0-9].*: find any non-numeric characters and then any characters that follow that
                 $x = preg_replace('#(?<!^)(?:-).*|(?<=^|-)0*|[^-0-9].*#', '', $x);
-                if (!strlen($x)) {
+                if (!strlen($x) || $x == '-') {
                     $x = '0';
                 }
 
diff --git a/tests/Unit/Math/BigInteger/TestCase.php b/tests/Unit/Math/BigInteger/TestCase.php
index 92c72222..132031f8 100644
--- a/tests/Unit/Math/BigInteger/TestCase.php
+++ b/tests/Unit/Math/BigInteger/TestCase.php
@@ -411,5 +411,8 @@ abstract class Unit_Math_BigInteger_TestCase extends PhpseclibTestCase
     {
         $temp = $this->getInstance('00');
         $this->assertSame($temp->toString(), '0');
+
+        $temp = $this->getInstance('-0');
+        $this->assertSame($temp->toString(), '0');
     }
 }