diff --git a/system/Commands/Encryption/GenerateKey.php b/system/Commands/Encryption/GenerateKey.php
index 7a0d47d0d542..3726360fa8ad 100644
--- a/system/Commands/Encryption/GenerateKey.php
+++ b/system/Commands/Encryption/GenerateKey.php
@@ -171,36 +171,41 @@ protected function writeNewEncryptionKeyToFile(string $oldKey, string $newKey):
         }
 
         $oldFileContents = (string) file_get_contents($envFile);
-        $replacementKey  = "\nencryption.key = {$newKey}";
 
-        if (! str_contains($oldFileContents, 'encryption.key')) {
-            return file_put_contents($envFile, $replacementKey, FILE_APPEND) !== false;
+        // Match an active setting line, preserving any leading whitespace and `export` prefix.
+        $activePattern = $this->keyPattern($oldKey);
+
+        if (preg_match($activePattern, $oldFileContents) === 1) {
+            $newFileContents = (string) preg_replace($activePattern, '$1' . $newKey, $oldFileContents, 1);
+
+            return file_put_contents($envFile, $newFileContents) !== false;
         }
 
-        $newFileContents = preg_replace($this->keyPattern($oldKey), $replacementKey, $oldFileContents);
+        // Match a commented-out setting line (e.g., from the shipped `env` template) and
+        // uncomment it. The optional `export` prefix is dropped on uncomment for predictability.
+        $commentedPattern = '/^\h*#\h*(?:export\h+)?encryption\.key\h*=\h*[^\r\n]*$/m';
 
-        if ($newFileContents === $oldFileContents) {
-            $newFileContents = preg_replace(
-                '/^[#\s]*encryption.key[=\s]*(?:hex2bin\:[a-f0-9]{64}|base64\:(?:[A-Za-z0-9+\/]{4})*(?:[A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=)?)$/m',
-                $replacementKey,
-                $oldFileContents,
-            );
+        if (preg_match($commentedPattern, $oldFileContents) === 1) {
+            $newFileContents = (string) preg_replace($commentedPattern, "encryption.key = {$newKey}", $oldFileContents, 1);
+
+            return file_put_contents($envFile, $newFileContents) !== false;
         }
 
-        return file_put_contents($envFile, $newFileContents) !== false;
+        // No setting present (active or commented); append.
+        return file_put_contents($envFile, "\nencryption.key = {$newKey}", FILE_APPEND) !== false;
     }
 
     /**
-     * Get the regex of the current encryption key.
+     * Returns the regex used to locate an active `encryption.key = ...` setting in the `.env`
+     * contents. The single capture group spans everything up to (and including) the `=` and any
+     * separating whitespace, so a `preg_replace` substitution preserves an optional `export`
+     * prefix while rewriting only the value.
+     *
+     * The `$oldKey` parameter is retained for backward compatibility with subclasses that
+     * override this method; it is no longer consulted because the pattern matches any value.
      */
     protected function keyPattern(string $oldKey): string
     {
-        $escaped = preg_quote($oldKey, '/');
-
-        if ($escaped !== '') {
-            $escaped = "[{$escaped}]*";
-        }
-
-        return "/^[#\\s]*encryption.key[=\\s]*{$escaped}$/m";
+        return '/^(\h*(?:export\h+)?encryption\.key\h*=\h*)[^\r\n]*$/m';
     }
 }
diff --git a/tests/system/Commands/Encryption/GenerateKeyTest.php b/tests/system/Commands/Encryption/GenerateKeyTest.php
index a4fb452fd5a2..387bdf7a1641 100644
--- a/tests/system/Commands/Encryption/GenerateKeyTest.php
+++ b/tests/system/Commands/Encryption/GenerateKeyTest.php
@@ -169,4 +169,40 @@ public function testKeyGenerateWhenNewBase64KeyIsSubsequentlyCommentedOut(): voi
         $this->assertStringContainsString('was successfully set.', $this->getBuffer());
         $this->assertNotSame($key, env('encryption.key', $key), 'Failed replacing the commented out key.');
     }
+
+    public function testKeyGenerateReplacesExportPrefixedEncryptionKey(): void
+    {
+        $existingKey = 'hex2bin:' . str_repeat('a', 64);
+        file_put_contents($this->envPath, "export encryption.key = {$existingKey}\n");
+
+        command('key:generate --force');
+
+        $contents = (string) file_get_contents($this->envPath);
+        $this->assertMatchesRegularExpression(
+            '/^export encryption\.key = hex2bin:[a-f0-9]{64}$/m',
+            $contents,
+            'The `export` prefix should be preserved and the value rewritten.',
+        );
+        $this->assertStringNotContainsString($existingKey, $contents, 'The old key value should be replaced.');
+    }
+
+    public function testKeyGenerateNotFooledByCommentMentioningEncryptionKey(): void
+    {
+        $envContents = "# Note: encryption.key is set automatically by spark key:generate.\n";
+        file_put_contents($this->envPath, $envContents);
+
+        command('key:generate --force');
+
+        $contents = (string) file_get_contents($this->envPath);
+        $this->assertStringContainsString(
+            $envContents,
+            $contents,
+            'The doc comment must be left intact.',
+        );
+        $this->assertMatchesRegularExpression(
+            '/^encryption\.key = hex2bin:[a-f0-9]{64}$/m',
+            $contents,
+            'A real `encryption.key` setting must be appended even when a comment mentions the name.',
+        );
+    }
 }
diff --git a/user_guide_src/source/changelogs/v4.7.3.rst b/user_guide_src/source/changelogs/v4.7.3.rst
index 469a2e8637a0..b7ba0d8d5ed3 100644
--- a/user_guide_src/source/changelogs/v4.7.3.rst
+++ b/user_guide_src/source/changelogs/v4.7.3.rst
@@ -40,6 +40,7 @@ Bugs Fixed
 - **CLI:** Fixed a bug where ``CLI::generateDimensions()`` leaked ``stty`` error output (e.g., ``stty: 'standard input': Inappropriate ioctl for device``) to stderr when stdin was not a TTY.
 - **CLI:** Fixed a bug where ``CLI::generateDimensions()`` leaked ``tput`` error output (``tput: No value for $TERM and no -T specified``) to stderr when the ``stty`` fallback was reached and the ``TERM`` environment variable was not set.
 - **Commands:** Fixed a bug in the ``env`` command where passing options only would cause the command to throw a ``TypeError`` instead of showing the current environment.
+- **Commands:** Fixed a bug in ``key:generate`` command where the regex used to locate the ``encryption.key`` line was fooled by a comment containing the substring (silently writing nothing), and did not handle DotEnv's ``export encryption.key = ...`` syntax.
 - **Common:** Fixed a bug where the ``command()`` helper function did not properly clean up output buffers, which could lead to risky tests when exceptions were thrown.
 - **Database:** Fixed a bug where the SQLSRV driver's decrement method was adding instead of subtracting the decrement value when ``$castTextToInt`` was false.
 - **Database:** Fixed a bug where the PostgreSQL driver's ``increment()`` and ``decrement()`` methods were not working for numeric columns.