diff --git a/phpseclib/Math/BigInteger.php b/phpseclib/Math/BigInteger.php
index 5cbb95aa..60e18866 100644
--- a/phpseclib/Math/BigInteger.php
+++ b/phpseclib/Math/BigInteger.php
@@ -2875,6 +2875,9 @@ class BigInteger
         // calculuate "not" without regard to $this->precision
         // (will always result in a smaller number.  ie. ~1 isn't 1111 1110 - it's 0)
         $temp = $this->toBytes();
+        if ($temp == '') {
+            return '';
+        }
         $pre_msb = decbin(ord($temp[0]));
         $temp = ~$temp;
         $msb = decbin(ord($temp[0]));
diff --git a/tests/Unit/Math/BigInteger/TestCase.php b/tests/Unit/Math/BigInteger/TestCase.php
index b960a338..338987b2 100644
--- a/tests/Unit/Math/BigInteger/TestCase.php
+++ b/tests/Unit/Math/BigInteger/TestCase.php
@@ -217,6 +217,11 @@ abstract class Unit_Math_BigInteger_TestCase extends PhpseclibTestCase
         $z = $this->getInstance('11111111111111111111111', 16);
 
         $this->assertSame($z->toHex(), $x->bitwise_NOT()->toHex());
+
+        $a = $this->getInstance(0);
+        $a->bitwise_not();
+
+        $this->assertSame($a->toString(), '0');
     }
 
     public function testBitwiseLeftShift()