diff --git a/.php_cs.dist b/.php_cs.dist
index 755afc0..41a47c3 100644
--- a/.php_cs.dist
+++ b/.php_cs.dist
@@ -193,6 +193,6 @@ return PhpCsFixer\Config::create()
                 'property',
             ],
         ],
-        'void_return' => true,
+        'void_return' => false,
         'whitespace_after_comma_in_array' => true,
     ]);
diff --git a/ChangeLog.md b/ChangeLog.md
index 6de6c5a..b0aa9f3 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -2,6 +2,12 @@
 
 All notable changes are documented in this file using the [Keep a CHANGELOG](http://keepachangelog.com/) principles.
 
+## [4.0.2] - 2020-06-15
+
+### Fixed
+
+* [#53](https://github.com/sebastianbergmann/comparator/issues/85): Version 4.0.1 breaks backward compatibility
+
 ## [4.0.1] - 2020-06-15
 
 ### Changed
@@ -62,6 +68,7 @@ All notable changes are documented in this file using the [Keep a CHANGELOG](htt
 * Added `SebastianBergmann\Comparator\Factory::reset()` to unregister all non-default comparators
 * Added support for `phpunit/phpunit-mock-objects` version `^5.0`
 
+[4.0.2]: https://github.com/sebastianbergmann/comparator/compare/4.0.1...4.0.2
 [4.0.1]: https://github.com/sebastianbergmann/comparator/compare/4.0.0...4.0.1
 [4.0.0]: https://github.com/sebastianbergmann/comparator/compare/3.0.2...4.0.0
 [3.0.2]: https://github.com/sebastianbergmann/comparator/compare/3.0.1...3.0.2
diff --git a/src/ArrayComparator.php b/src/ArrayComparator.php
index a13add8..9f1c399 100644
--- a/src/ArrayComparator.php
+++ b/src/ArrayComparator.php
@@ -43,7 +43,7 @@ public function accepts($expected, $actual)
      *
      * @throws ComparisonFailure
      */
-    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false, array &$processed = []): void
+    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false, array &$processed = [])/*: void*/
     {
         if ($canonicalize) {
             \sort($expected);
diff --git a/src/Comparator.php b/src/Comparator.php
index 8534e7f..e1906c1 100644
--- a/src/Comparator.php
+++ b/src/Comparator.php
@@ -31,7 +31,7 @@ public function __construct()
         $this->exporter = new Exporter;
     }
 
-    public function setFactory(Factory $factory): void
+    public function setFactory(Factory $factory)/*: void*/
     {
         $this->factory = $factory;
     }
diff --git a/src/DOMNodeComparator.php b/src/DOMNodeComparator.php
index 558e740..ac6f1e8 100644
--- a/src/DOMNodeComparator.php
+++ b/src/DOMNodeComparator.php
@@ -42,7 +42,7 @@ public function accepts($expected, $actual)
      *
      * @throws ComparisonFailure
      */
-    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false, array &$processed = []): void
+    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false, array &$processed = [])/*: void*/
     {
         $expectedAsString = $this->nodeToText($expected, true, $ignoreCase);
         $actualAsString   = $this->nodeToText($actual, true, $ignoreCase);
diff --git a/src/DateTimeComparator.php b/src/DateTimeComparator.php
index 1222ed5..3d28e70 100644
--- a/src/DateTimeComparator.php
+++ b/src/DateTimeComparator.php
@@ -41,7 +41,7 @@ public function accepts($expected, $actual)
      * @throws \Exception
      * @throws ComparisonFailure
      */
-    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false, array &$processed = []): void
+    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false, array &$processed = [])/*: void*/
     {
         /** @var \DateTimeInterface $expected */
         /** @var \DateTimeInterface $actual */
diff --git a/src/DoubleComparator.php b/src/DoubleComparator.php
index cf90366..a851c7a 100644
--- a/src/DoubleComparator.php
+++ b/src/DoubleComparator.php
@@ -45,7 +45,7 @@ public function accepts($expected, $actual)
      *
      * @throws ComparisonFailure
      */
-    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false): void
+    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false)/*: void*/
     {
         if ($delta == 0) {
             $delta = self::EPSILON;
diff --git a/src/Factory.php b/src/Factory.php
index de70229..7131f38 100644
--- a/src/Factory.php
+++ b/src/Factory.php
@@ -84,7 +84,7 @@ public function getComparatorFor($expected, $actual)
      *
      * @param Comparator $comparator The comparator to be registered
      */
-    public function register(Comparator $comparator): void
+    public function register(Comparator $comparator)/*: void*/
     {
         \array_unshift($this->customComparators, $comparator);
 
@@ -98,7 +98,7 @@ public function register(Comparator $comparator): void
      *
      * @param Comparator $comparator The comparator to be unregistered
      */
-    public function unregister(Comparator $comparator): void
+    public function unregister(Comparator $comparator)/*: void*/
     {
         foreach ($this->customComparators as $key => $_comparator) {
             if ($comparator === $_comparator) {
@@ -110,7 +110,7 @@ public function unregister(Comparator $comparator): void
     /**
      * Unregisters all non-default comparators.
      */
-    public function reset(): void
+    public function reset()/*: void*/
     {
         $this->customComparators = [];
     }
diff --git a/src/NumericComparator.php b/src/NumericComparator.php
index 31d8050..61537ca 100644
--- a/src/NumericComparator.php
+++ b/src/NumericComparator.php
@@ -42,7 +42,7 @@ public function accepts($expected, $actual)
      *
      * @throws ComparisonFailure
      */
-    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false): void
+    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false)/*: void*/
     {
         if ($this->isInfinite($actual) && $this->isInfinite($expected)) {
             return;
diff --git a/src/ObjectComparator.php b/src/ObjectComparator.php
index 7a9612a..f3b7dac 100644
--- a/src/ObjectComparator.php
+++ b/src/ObjectComparator.php
@@ -39,7 +39,7 @@ public function accepts($expected, $actual)
      *
      * @throws ComparisonFailure
      */
-    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false, array &$processed = []): void
+    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false, array &$processed = [])/*: void*/
     {
         if (\get_class($actual) !== \get_class($expected)) {
             throw new ComparisonFailure(
diff --git a/src/ResourceComparator.php b/src/ResourceComparator.php
index 4ffe931..fcd1edf 100644
--- a/src/ResourceComparator.php
+++ b/src/ResourceComparator.php
@@ -38,7 +38,7 @@ public function accepts($expected, $actual)
      *
      * @throws ComparisonFailure
      */
-    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false): void
+    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false)/*: void*/
     {
         if ($actual != $expected) {
             throw new ComparisonFailure(
diff --git a/src/ScalarComparator.php b/src/ScalarComparator.php
index 8043c0e..3f3ccc1 100644
--- a/src/ScalarComparator.php
+++ b/src/ScalarComparator.php
@@ -44,7 +44,7 @@ public function accepts($expected, $actual)
      *
      * @throws ComparisonFailure
      */
-    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false): void
+    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false)/*: void*/
     {
         $expectedToCompare = $expected;
         $actualToCompare   = $actual;
diff --git a/src/SplObjectStorageComparator.php b/src/SplObjectStorageComparator.php
index d9c6b19..01fcebb 100644
--- a/src/SplObjectStorageComparator.php
+++ b/src/SplObjectStorageComparator.php
@@ -38,7 +38,7 @@ public function accepts($expected, $actual)
      *
      * @throws ComparisonFailure
      */
-    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false): void
+    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false)/*: void*/
     {
         foreach ($actual as $object) {
             if (!$expected->contains($object)) {
diff --git a/src/TypeComparator.php b/src/TypeComparator.php
index 18b2850..9131fb8 100644
--- a/src/TypeComparator.php
+++ b/src/TypeComparator.php
@@ -38,7 +38,7 @@ public function accepts($expected, $actual)
      *
      * @throws ComparisonFailure
      */
-    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false): void
+    public function assertEquals($expected, $actual, $delta = 0.0, $canonicalize = false, $ignoreCase = false)/*: void*/
     {
         if (\gettype($expected) != \gettype($actual)) {
             throw new ComparisonFailure(