diff --git a/docs/guides/divi-shortform.md b/docs/guides/divi-shortform.md
index 8ca822a..d20d59a 100644
--- a/docs/guides/divi-shortform.md
+++ b/docs/guides/divi-shortform.md
@@ -25,8 +25,8 @@ Neue Divi-Inhalte beschreibt man als JSON-Knoten. `lit-divi-insert` (in `nodes`)
   `section_type: "fullwidth"` für Vollbreite-Abschnitte (dann nur `fullwidth-…`-Module in `modules`);
   `background_color`. Spezialabschnitte (specialty) nur im Divi-Builder bauen.
 - **Zeile** (`row`): `columns` = Breiten als Brüche, die zusammen 1 ergeben (`"4_4"`, `"1_2,1_2"`,
-  `"1_3,2_3"`, `"1_4,1_4,1_2"`, auch Fünftel); `modules` = je Spalte eine Liste (bei einer Spalte reicht eine
-  einfache Liste).
+  `"1_3,2_3"`, `"1_4,1_4,1_2"`, auch `1_5`, `2_5`, `3_5` wie im Divi-Builder – `4_5` nicht); `modules` = je
+  Spalte eine Liste (bei einer Spalte reicht eine einfache Liste).
 - **Module** mit Kind-Modulen (Akkordeon, Tabs, Slider, Kontaktformular, Karte, Social-Media-Follow,
   Icon-Liste) bekommen ihre Einträge in `items`; der Eintragstyp ergibt sich von selbst.
 - `label` fehlt → Admin-Label „<Abschnitt> – <Modul>“, z. B. „Hero – Button“. Abschnitten deshalb ein Label
@@ -90,7 +90,9 @@ Fehler: `validation_failed` bzw. `invalid_attr_path` mit `fields` (Eingabepfad 
 
 Die Breite einer Spalte steht in `module.decoration.sizing` (Desktop: `flexType`, z. B. `8_24` = 1/3). Wer
 diesen Desktop-Wert über `attrs` ersetzt, ersetzt das ganze Objekt: `flexType` immer mitschicken, sonst fällt
-die Breite weg. In einer Zeile mit festen Breiten alle Spalten zusammen ändern (Summe 1). Die Angabe
+die Breite weg. Erlaubt sind je Breakpoint (Desktop, Tablet, Telefon, …) nur die Spaltenklassen des
+Divi-Builders: `1_24` … `24_24`, `1_5`, `2_5`, `3_5`, `1_7`, `1_9`, `1_10`, `1_11` oder `none`. In einer Zeile
+mit festen Breiten alle Spalten zusammen ändern (Summe 1). Die Angabe
 `flexColumnStructure` der Zeile (Spaltenvorlage im Divi-Builder) passt das Werkzeug nicht an; nach einer
 Breitenänderung zeigt der Builder dort evtl. noch die alte Vorlage; gespeichert sind die neuen Breiten (bei
 Bedarf die Vorlage im Builder neu wählen).
diff --git a/src/Integrations/Divi/Compose/ColumnWidths.php b/src/Integrations/Divi/Compose/ColumnWidths.php
index 173afa9..87af38a 100644
--- a/src/Integrations/Divi/Compose/ColumnWidths.php
+++ b/src/Integrations/Divi/Compose/ColumnWidths.php
@@ -10,13 +10,16 @@ use LIT\MCP\Integrations\Divi\BlockTree\NodeIndex;
 
 /**
  * Column widths of Divi rows (pure, static): the "columns" input of new rows
- * ("1_3,2_3" → flexTypes, ruling S34) and the desktop flexType checks on update (rulings S41,
- * S43). Every width this class returns is built from digits or taken from a fixed list.
+ * ("1_3,2_3" → flexTypes, ruling S34) and the flexType checks on update (rulings S41, S43,
+ * S49). Every width this class returns is built from digits or taken from a fixed list.
  */
 final class ColumnWidths
 {
-    /** Column fractions Divi's flex layout knows besides multiples of 1/24. */
-    private const SPECIAL_WIDTHS = ['1_5', '2_5', '3_5', '4_5', '1_7', '1_9', '1_10', '1_11'];
+    /**
+     * Column fractions of "columns" besides multiples of 1/24: the builder's special column
+     * classes (ruling S49 – no 4_5, the builder does not offer it).
+     */
+    private const SPECIAL_WIDTHS = ['1_5', '2_5', '3_5', '1_7', '1_9', '1_10', '1_11'];
 
     /**
      * The builder's "Column Class" choices (Divi 5.2.1 visual-builder/build/field-library.js):
@@ -29,6 +32,8 @@ final class ColumnWidths
     /** Divi's column default (column/module-default-render-attributes.json). */
     private const DEFAULT_WIDTH = '24_24';
 
+    private const CLASS_LIST = '1_24 … 24_24, 1_5, 2_5, 3_5, 1_7, 1_9, 1_10, 1_11 oder none';
+
     private const FORMAT = 'Spaltenaufteilung wie "1_2,1_2" oder "1_3,2_3" erwartet';
 
     private const FULL_ROW = 'die Spaltenbreiten müssen zusammen eine volle Zeile ergeben (z. B. "1_3,2_3")';
@@ -100,12 +105,13 @@ final class ColumnWidths
     }
 
     /**
-     * Column widths on update (rulings S41, S43). Every new desktop flexType must be one of the
-     * builder's column classes (isColumnClass()) or null (removed: Divi's default 24_24). The
-     * row sum is only checked for rows that are exact today – every column has a class other
-     * than "none", the classes fill the row (rowError()), the row does not wrap or use a grid
-     * on desktop – and when no new width is "none". Such a row must stay exact after all
-     * changes; other rows are laid out by Divi as the builder allows.
+     * Column widths on update (rulings S41, S43, S49). Every new flexType – desktop and every
+     * other breakpoint – must be one of the builder's column classes (isColumnClass()) or null
+     * (removed; desktop then is Divi's default 24_24). The desktop row sum is only checked for
+     * rows that are exact today – every column has a class other than "none", the classes fill
+     * the row (rowError()), the row does not wrap or use a grid on desktop – and when no new
+     * width is "none". Such a row must stay exact after all changes; other rows are laid out by
+     * Divi as the builder allows.
      *
      * @param list<array{0: Block, 1: array<string, mixed>, 2: string}> $updates Block, its new attrs, input path.
      * @return array<string, string>
@@ -116,14 +122,27 @@ final class ColumnWidths
         $new = [];
         $rows = [];
         foreach ($updates as [$block, $attrs, $field]) {
+            if ($block->name() !== 'divi/column') {
+                continue;
+            }
+
+            $breakpoint = self::invalidBreakpoint($block->attrs(), $attrs);
+            if ($breakpoint !== null) {
+                $errors[$field . '.attrs.' . self::SIZING] = sprintf(
+                    'Spaltenbreite (flexType) für %s wie im Divi-Builder erwartet: %s',
+                    $breakpoint,
+                    self::CLASS_LIST
+                );
+            }
+
             $width = self::width($attrs);
-            if ($block->name() !== 'divi/column' || $width === self::width($block->attrs())) {
+            if ($width === self::width($block->attrs())) {
                 continue;
             }
 
             if ($width !== null && ! self::isColumnClass($width)) {
                 $errors[$field . '.attrs.' . self::SIZING] = 'Spaltenbreite (flexType) wie im Divi-Builder erwartet: '
-                    . '1_24 … 24_24, 1_5, 2_5, 3_5, 1_7, 1_9, 1_10, 1_11 oder none';
+                    . self::CLASS_LIST;
                 continue;
             }
 
@@ -172,10 +191,34 @@ final class ColumnWidths
         return self::rowError($widths) === null;
     }
 
-    /** @param array<string, mixed> $attrs */
-    private static function width(array $attrs): mixed
+    /**
+     * The first non-desktop breakpoint whose flexType changed to something that is no column
+     * class (ruling S49), or null.
+     *
+     * @param array<string, mixed> $before
+     * @param array<string, mixed> $after
+     */
+    private static function invalidBreakpoint(array $before, array $after): ?string
     {
-        $sizing = AttrMap::desktop($attrs, self::SIZING);
+        foreach (AttrMap::BREAKPOINTS as $breakpoint) {
+            if ($breakpoint === 'desktop') {
+                continue;
+            }
+
+            $width = self::width($after, $breakpoint);
+            if ($width !== null && $width !== self::width($before, $breakpoint) && ! self::isColumnClass($width)) {
+                return $breakpoint;
+            }
+        }
+
+        return null;
+    }
+
+    /** @param array<string, mixed> $attrs */
+    private static function width(array $attrs, string $breakpoint = 'desktop'): mixed
+    {
+        $map = AttrMap::get($attrs, self::SIZING);
+        $sizing = is_array($map) && is_array($map[$breakpoint] ?? null) ? ($map[$breakpoint]['value'] ?? null) : null;
 
         return is_array($sizing) ? ($sizing['flexType'] ?? null) : null;
     }
diff --git a/tests/Unit/Integrations/Divi/Compose/ColumnWidthsTest.php b/tests/Unit/Integrations/Divi/Compose/ColumnWidthsTest.php
index 8cb4e22..ea02505 100644
--- a/tests/Unit/Integrations/Divi/Compose/ColumnWidthsTest.php
+++ b/tests/Unit/Integrations/Divi/Compose/ColumnWidthsTest.php
@@ -29,6 +29,14 @@ final class ColumnWidthsTest extends TestCase
         self::assertStringContainsString('volle Zeile', (string) ColumnWidths::parse('1_2,1_3')['error']);
     }
 
+    /** Ruling S49: new rows use only widths the builder offers – 4_5 is no builder column class. */
+    public function testFourFifthsIsNoInsertWidth(): void
+    {
+        self::assertSame(['widths' => ['24_24'], 'error' => 'Spaltenbreite 4_5 gibt es in Divi nicht'], ColumnWidths::parse('1_5,4_5'));
+        self::assertNotNull(ColumnWidths::rowError(['1_5', '4_5']));
+        self::assertSame(['widths' => ['1_5', '2_5', '2_5'], 'error' => null], ColumnWidths::parse('1_5,2_5,2_5'));
+    }
+
     /** Ruling S43: the builder's column classes. */
     public function testColumnClassesAreTheBuilderList(): void
     {
diff --git a/tests/Unit/Integrations/Divi/Pages/DiviUpdateAbilityTest.php b/tests/Unit/Integrations/Divi/Pages/DiviUpdateAbilityTest.php
index 3ddb687..b3b24ee 100644
--- a/tests/Unit/Integrations/Divi/Pages/DiviUpdateAbilityTest.php
+++ b/tests/Unit/Integrations/Divi/Pages/DiviUpdateAbilityTest.php
@@ -157,6 +157,38 @@ final class DiviUpdateAbilityTest extends DiviWriteAbilityTestCase
         self::assertSame([], $this->saved);
     }
 
+    /** Ruling S49: tablet/phone (every non-desktop breakpoint) flexTypes are format-checked like desktop. */
+    public function testUpdateChecksTheColumnClassFormatOnOtherBreakpoints(): void
+    {
+        foreach (['tablet', 'phone', 'phoneWide'] as $breakpoint) {
+            foreach (['4_5', '13_25', 'auto'] as $width) {
+                $result = $this->update()->execute(['post_id' => 7, 'tree_rev' => $this->treeRev(), 'changes' => [[
+                    'id' => 's0.r0.c0',
+                    'attrs' => ['module.decoration.sizing' => [
+                        'desktop' => ['flexType' => '8_24'],
+                        $breakpoint => ['flexType' => $width],
+                    ]],
+                ]]]);
+                self::assertInstanceOf(WP_Error::class, $result, $breakpoint . ' ' . $width);
+                $message = self::clientError($result)['fields']['changes[0].attrs.module.decoration.sizing'];
+                self::assertStringContainsString($breakpoint, $message);
+                self::assertStringContainsString('none', $message);
+            }
+        }
+        self::assertSame([], $this->saved);
+
+        $valid = $this->update()->execute(['post_id' => 7, 'tree_rev' => $this->treeRev(), 'changes' => [[
+            'id' => 's0.r0.c0',
+            'attrs' => ['module.decoration.sizing' => [
+                'desktop' => ['flexType' => '8_24'],
+                'tablet' => ['flexType' => '24_24'],
+                'phone' => ['flexType' => 'none'],
+            ]],
+        ]]]);
+        self::assertTrue($valid['ok'], (string) json_encode($valid));
+        self::assertStringContainsString('"tablet":{"value":{"flexType":"24_24"}},"phone":{"value":{"flexType":"none"}}', $this->saved[0]);
+    }
+
     /** Ruling S43: rows that are no plain exact row are not sum-checked (none, omitted width, wrap). */
     public function testUpdateAcceptsWidthChangesInLooseRows(): void
     {