diff --git a/phpseclib/Math/BigInteger/Engines/GMP.php b/phpseclib/Math/BigInteger/Engines/GMP.php
index 262e55c2..8dbb85a2 100644
--- a/phpseclib/Math/BigInteger/Engines/GMP.php
+++ b/phpseclib/Math/BigInteger/Engines/GMP.php
@@ -517,7 +517,14 @@ class GMP extends Engine
         $result->bitmask = $this->bitmask;
 
         if ($result->bitmask !== false) {
+            $flip = $result->value < 0;
+            if ($flip) {
+                $result->value = -$result->value;
+            }
             $result->value = $result->value & $result->bitmask->value;
+            if ($flip) {
+                $result->value = -$result->value;
+            }
         }
 
         return $result;
diff --git a/phpseclib/Math/BigInteger/Engines/PHP.php b/phpseclib/Math/BigInteger/Engines/PHP.php
index a313b484..24226952 100644
--- a/phpseclib/Math/BigInteger/Engines/PHP.php
+++ b/phpseclib/Math/BigInteger/Engines/PHP.php
@@ -157,6 +157,7 @@ abstract class PHP extends Engine
         }
 
         $temp = clone $this;
+        $temp->bitmask = false;
         $temp->is_negative = false;
 
         $divisor = new static();
diff --git a/tests/Unit/Math/BigInteger/TestCase.php b/tests/Unit/Math/BigInteger/TestCase.php
index 56d2234d..c8445238 100644
--- a/tests/Unit/Math/BigInteger/TestCase.php
+++ b/tests/Unit/Math/BigInteger/TestCase.php
@@ -485,4 +485,21 @@ abstract class Unit_Math_BigInteger_TestCase extends PhpseclibTestCase
         $temp = $this->getInstance('-0');
         $this->assertSame($temp->toString(), '0');
     }
+
+    public function testNegativePrecision()
+    {
+        $vals = [
+            '-9223372036854775808', // eg. 8000 0000 0000 0000
+            '-1'
+        ];
+        foreach ($vals as $val) {
+            $x = $this->getInstance($val);
+            $x->setPrecision(64); // ie. 8 bytes
+            $this->assertSame($val, "$x");
+            $r = $x->toBytes(true);
+            $this->assertSame(8, strlen($r));
+            $x2 = $this->getInstance($r, -256);
+            $this->assertSame(0, $x->compare($x2));
+        }
+    }
 }