diff --git a/phpseclib/Math/BigInteger.php b/phpseclib/Math/BigInteger.php
index c1e239cb..e818e8bb 100644
--- a/phpseclib/Math/BigInteger.php
+++ b/phpseclib/Math/BigInteger.php
@@ -413,7 +413,10 @@ class Math_BigInteger {
                 break;
             case  10:
             case -10:
-                $x = preg_replace('#^(-?[0-9]*).*#', '$1', $x);
+                // (?<!^)(?:-).*: find any -'s that aren't at the beginning and then any characters that follow that
+                // (?<=^|-)0*: find any 0's that are preceeded 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);
 
                 switch ( MATH_BIGINTEGER_MODE ) {
                     case MATH_BIGINTEGER_MODE_GMP: