diff --git a/src/Spout/Common/Entity/Style/Style.php b/src/Spout/Common/Entity/Style/Style.php
index f4beb97..2bacc7a 100644
--- a/src/Spout/Common/Entity/Style/Style.php
+++ b/src/Spout/Common/Entity/Style/Style.php
@@ -490,13 +490,13 @@ class Style
         return $this->isRegistered;
     }
 
-    public function register(int $id) : void
+    public function markAsRegistered(?int $id) : void
     {
         $this->setId($id);
         $this->isRegistered = true;
     }
 
-    public function unregister() : void
+    public function unmarkAsRegistered() : void
     {
         $this->setId(0);
         $this->isRegistered = false;
diff --git a/src/Spout/Writer/Common/Manager/Style/StyleManagerInterface.php b/src/Spout/Writer/Common/Manager/Style/StyleManagerInterface.php
index be77110..6d01bd5 100644
--- a/src/Spout/Writer/Common/Manager/Style/StyleManagerInterface.php
+++ b/src/Spout/Writer/Common/Manager/Style/StyleManagerInterface.php
@@ -24,7 +24,7 @@ interface StyleManagerInterface
      * Typically, set "wrap text" if a cell contains a new line.
      *
      * @param Cell $cell
-     * @return ManagedStyle|null The eventually updated style
+     * @return ManagedStyle The eventually updated style
      */
     public function applyExtraStylesIfNeeded(Cell $cell) : ManagedStyle;
 }
diff --git a/src/Spout/Writer/Common/Manager/Style/StyleRegistry.php b/src/Spout/Writer/Common/Manager/Style/StyleRegistry.php
index dcfa267..6b439a7 100644
--- a/src/Spout/Writer/Common/Manager/Style/StyleRegistry.php
+++ b/src/Spout/Writer/Common/Manager/Style/StyleRegistry.php
@@ -38,7 +38,7 @@ class StyleRegistry
 
         if (!$this->hasSerializedStyleAlreadyBeenRegistered($serializedStyle)) {
             $nextStyleId = \count($this->serializedStyleToStyleIdMappingTable);
-            $style->register($nextStyleId);
+            $style->markAsRegistered($nextStyleId);
 
             $this->serializedStyleToStyleIdMappingTable[$serializedStyle] = $nextStyleId;
             $this->styleIdToStyleMappingTable[$nextStyleId] = $style;
@@ -47,19 +47,6 @@ class StyleRegistry
         return $this->getStyleFromSerializedStyle($serializedStyle);
     }
 
-    /**
-     * Returns whether the given style has already been registered.
-     *
-     * @param Style $style
-     * @return bool
-     */
-    protected function hasStyleAlreadyBeenRegistered(Style $style)
-    {
-        $serializedStyle = $this->serialize($style);
-
-        return $this->hasSerializedStyleAlreadyBeenRegistered($serializedStyle);
-    }
-
     /**
      * Returns whether the serialized style has already been registered.
      *
@@ -114,11 +101,11 @@ class StyleRegistry
     {
         // In order to be able to properly compare style, set static ID value and reset registration
         $currentId = $style->getId();
-        $style->unregister();
+        $style->unmarkAsRegistered();
 
         $serializedStyle = \serialize($style);
 
-        $style->setId($currentId);
+        $style->markAsRegistered($currentId);
 
         return $serializedStyle;
     }
diff --git a/src/Spout/Writer/ODS/Manager/WorksheetManager.php b/src/Spout/Writer/ODS/Manager/WorksheetManager.php
index 894c82f..1997e9e 100644
--- a/src/Spout/Writer/ODS/Manager/WorksheetManager.php
+++ b/src/Spout/Writer/ODS/Manager/WorksheetManager.php
@@ -165,7 +165,8 @@ class WorksheetManager implements WorksheetManagerInterface
             if ($managedStyle->isUpdated()) {
                 $registeredStyle = $this->styleManager->registerStyle($managedStyle->getStyle());
             } else {
-                $registeredStyle = $rowStyle = $this->styleManager->registerStyle($rowStyle);
+                $registeredStyle = $this->styleManager->registerStyle($rowStyle);
+                $rowStyle = $registeredStyle;
             }
         } else {
             $mergedCellAndRowStyle = $this->styleMerger->merge($cell->getStyle(), $rowStyle);
diff --git a/src/Spout/Writer/XLSX/Manager/WorksheetManager.php b/src/Spout/Writer/XLSX/Manager/WorksheetManager.php
index d68d8f3..3a210d6 100644
--- a/src/Spout/Writer/XLSX/Manager/WorksheetManager.php
+++ b/src/Spout/Writer/XLSX/Manager/WorksheetManager.php
@@ -193,7 +193,8 @@ EOD;
             if ($managedStyle->isUpdated()) {
                 $registeredStyle = $this->styleManager->registerStyle($managedStyle->getStyle());
             } else {
-                $registeredStyle = $rowStyle = $this->styleManager->registerStyle($rowStyle);
+                $registeredStyle = $this->styleManager->registerStyle($rowStyle);
+                $rowStyle = $registeredStyle;
             }
         } else {
             $mergedCellAndRowStyle = $this->styleMerger->merge($cell->getStyle(), $rowStyle);