diff --git a/phpseclib/Math/BigInteger.php b/phpseclib/Math/BigInteger.php
index 9082ad5f..da79b031 100644
--- a/phpseclib/Math/BigInteger.php
+++ b/phpseclib/Math/BigInteger.php
@@ -441,6 +441,9 @@ class Math_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)) {
+                    $x = '0';
+                }
 
                 switch (MATH_BIGINTEGER_MODE) {
                     case MATH_BIGINTEGER_MODE_GMP: