diff --git a/src/BigDecimal.php b/src/BigDecimal.php
index 45e3cf8..ecf1336 100644
--- a/src/BigDecimal.php
+++ b/src/BigDecimal.php
@@ -670,6 +670,10 @@ class BigDecimal implements \Serializable
      */
     public function unserialize($value)
     {
+        if ($this->value !== null || $this->scale !== null) {
+            throw new \LogicException('unserialize() is an internal function, it must not be called directly.');
+        }
+
         list ($value, $scale) = explode(':', $value);
 
         $this->value = $value;
diff --git a/src/BigInteger.php b/src/BigInteger.php
index 683e345..14bc6a2 100644
--- a/src/BigInteger.php
+++ b/src/BigInteger.php
@@ -562,16 +562,20 @@ class BigInteger implements \Serializable
     /**
      * This method is required by interface Serializable and MUST NOT be accessed directly.
      *
-     * Accessing this method directly would bypass consistency checks and break immutability.
-     *
      * @internal
      *
      * @param string $value
      *
      * @return void
+     *
+     * @throws \LogicException
      */
     public function unserialize($value)
     {
+        if ($this->value !== null) {
+            throw new \LogicException('unserialize() is an internal function, it must not be called directly.');
+        }
+
         $this->value = $value;
     }
 }
diff --git a/tests/BigDecimalTest.php b/tests/BigDecimalTest.php
index c112507..0e02c04 100644
--- a/tests/BigDecimalTest.php
+++ b/tests/BigDecimalTest.php
@@ -1956,4 +1956,12 @@ class BigDecimalTest extends AbstractTestCase
 
         $this->assertBigDecimalEquals($value, $scale, unserialize(serialize($number)));
     }
+
+    /**
+     * @expectedException \LogicException
+     */
+    public function testDirectCallToUnserialize()
+    {
+        BigDecimal::zero()->unserialize('123:0');
+    }
 }
diff --git a/tests/BigIntegerTest.php b/tests/BigIntegerTest.php
index 6e6cac0..4c0a1b7 100644
--- a/tests/BigIntegerTest.php
+++ b/tests/BigIntegerTest.php
@@ -1577,4 +1577,12 @@ class BigIntegerTest extends AbstractTestCase
 
         $this->assertBigIntegerEquals($value, unserialize(serialize($number)));
     }
+
+    /**
+     * @expectedException \LogicException
+     */
+    public function testDirectCallToUnserialize()
+    {
+        BigInteger::zero()->unserialize('123');
+    }
 }