diff --git a/README.md b/README.md
index 76601f34..8da99532 100644
--- a/README.md
+++ b/README.md
@@ -345,3 +345,11 @@ add_filter('optml_dont_replace_url', function( $old, $url ) {
 
 }, 10, 2);
 </code>
+
+= Can I keep the sizes attribute I wrote for an image ? =
+
+Yes. Add the `data-optml-keep-sizes` attribute to the image tag and the page profiler won't add its own entries to the image's `sizes` attribute. Images lazy loaded by Optimole don't keep `srcset` or `sizes`, since the lazy loader doesn't need them. To keep the existing `sizes` attribute on every image, add this snippet:
+
+<code>
+add_filter( 'optml_keep_existing_sizes', '__return_true' );
+</code>
diff --git a/inc/tag_replacer.php b/inc/tag_replacer.php
index 3330edb2..0df7d581 100644
--- a/inc/tag_replacer.php
+++ b/inc/tag_replacer.php
@@ -13,6 +13,11 @@ final class Optml_Tag_Replacer extends Optml_App_Replacer {
 	use Optml_Validator;
 	use Optml_Dam_Offload_Utils;
 
+	/**
+	 * Attribute an image uses to keep its own sizes attribute.
+	 */
+	const KEEP_SIZES_ATTRIBUTE = 'data-optml-keep-sizes';
+
 	/**
 	 * Cached object instance.
 	 *
@@ -550,11 +555,16 @@ public function add_missing_srcset_attributes( $tag, $missing_srcsets, $new_url,
 			$tag = $this->insert_after_attribute( $tag, 'src', $srcset_attr );
 		}
 
-		// Handle sizes attribute - skip if existing sizes contains calc() or complex formulas
+		// Handle sizes attribute - skip if the image asks to keep its existing sizes, or they contain calc() or complex formulas
 		if ( ! empty( $new_sizes_entries ) ) {
 			$should_skip_sizes = false;
 
-			if ( $has_existing_sizes ) {
+			if ( $has_existing_sizes && $this->keeps_existing_sizes( $tag ) ) {
+				$should_skip_sizes = true;
+				if ( OPTML_DEBUG ) {
+					do_action( 'optml_log', 'Keeping the existing sizes attribute: ' . $new_url );
+				}
+			} elseif ( $has_existing_sizes ) {
 				// Check if existing sizes contains calc() or complex formulas
 				$sizes = $this->find_quoted_attribute( $tag, 'sizes' );
 				if ( null !== $sizes ) {
@@ -596,9 +606,9 @@ function ( $a, $b ) {
 					}
 				}
 			} else {
-				// Log that sizes were skipped due to complex formulas
+				// Log that sizes were skipped (kept on request, or complex formula)
 				if ( OPTML_DEBUG ) {
-					do_action( 'optml_log', 'Skipped adding sizes due to complex formula detection' );
+					do_action( 'optml_log', 'Skipped adding sizes' );
 				}
 			}
 		}
@@ -834,6 +844,28 @@ private function has_attribute( string $tag, string $name ): bool {
 		return in_array( $name, array_column( $this->get_attributes( $tag ) ?? [], 'name' ), true );
 	}
 
+	/**
+	 * Check whether an image's own sizes attribute must be left as it is.
+	 *
+	 * An image opts out with the data-optml-keep-sizes attribute. The optml_keep_existing_sizes filter
+	 * does it for every image, or for the ones it picks, with no change to the markup.
+	 *
+	 * @param string $tag The image tag.
+	 *
+	 * @return bool True if the existing sizes attribute is kept.
+	 */
+	private function keeps_existing_sizes( string $tag ): bool {
+		$keep = $this->has_attribute( $tag, self::KEEP_SIZES_ATTRIBUTE );
+
+		/**
+		 * Filters whether Optimole leaves an image's existing sizes attribute unchanged.
+		 *
+		 * @param bool   $keep Whether the existing sizes attribute is kept. True when the image has data-optml-keep-sizes.
+		 * @param string $tag  The image tag.
+		 */
+		return (bool) apply_filters( 'optml_keep_existing_sizes', $keep, $tag );
+	}
+
 	/**
 	 * Check whether the tag's src or srcset is a data: URI placeholder.
 	 *
diff --git a/readme.txt b/readme.txt
index 89ca3fab..da7c72b0 100755
--- a/readme.txt
+++ b/readme.txt
@@ -345,3 +345,11 @@ add_filter('optml_dont_replace_url', function( $old, $url ) {
 
 }, 10, 2);
 </code>
+
+= Can I keep the sizes attribute I wrote for an image ? =
+
+Yes. Add the `data-optml-keep-sizes` attribute to the image tag and the page profiler won't add its own entries to the image's `sizes` attribute. Images lazy loaded by Optimole don't keep `srcset` or `sizes`, since the lazy loader doesn't need them. To keep the existing `sizes` attribute on every image, add this snippet:
+
+<code>
+add_filter( 'optml_keep_existing_sizes', '__return_true' );
+</code>
diff --git a/tests/test-srcset.php b/tests/test-srcset.php
index 5b90d7d6..3f8c6b3d 100644
--- a/tests/test-srcset.php
+++ b/tests/test-srcset.php
@@ -168,6 +168,65 @@ public function test_add_missing_srcset_attributes_with_existing_sizes() {
 		$this->assertStringContainsString( '(max-width: 768px) 400px', $result );
 	}
 
+	/**
+	 * An image with data-optml-keep-sizes keeps its hand-written sizes, and still gets the new srcset entries.
+	 */
+	public function test_keep_sizes_attribute_preserves_existing_sizes() {
+		$tag_replacer = new Optml_Tag_Replacer();
+
+		$tag = '<img src="https://example.com/image.jpg" srcset="existing-300w.jpg 300w" sizes="(max-width: 480px) 300px" data-optml-keep-sizes alt="Test" />';
+		$missing_srcsets = [
+			[ 'w' => 200, 'h' => 150, 'd' => 1, 's' => '200w', 'b' => 320 ],
+			[ 'w' => 400, 'h' => 300, 'd' => 1, 's' => '400w', 'b' => 768 ],
+		];
+
+		$result = $tag_replacer->add_missing_srcset_attributes( $tag, $missing_srcsets, 'https://example.com/image.jpg', false );
+
+		$this->assertStringContainsString( 'sizes="(max-width: 480px) 300px"', $result );
+		$this->assertStringNotContainsString( '(max-width: 320px) 200px', $result );
+		$this->assertStringContainsString( '200w', $result );
+	}
+
+	/**
+	 * The optml_keep_existing_sizes filter keeps existing sizes site-wide, with no change to the markup.
+	 */
+	public function test_keep_existing_sizes_filter() {
+		$tag_replacer = new Optml_Tag_Replacer();
+
+		$tag = '<img src="https://example.com/image.jpg" srcset="existing-300w.jpg 300w" sizes="(max-width: 480px) 300px" alt="Test" />';
+		$missing_srcsets = [
+			[ 'w' => 200, 'h' => 150, 'd' => 1, 's' => '200w', 'b' => 320 ],
+		];
+
+		add_filter( 'optml_keep_existing_sizes', '__return_true' );
+		$result = $tag_replacer->add_missing_srcset_attributes( $tag, $missing_srcsets, 'https://example.com/image.jpg', false );
+		remove_filter( 'optml_keep_existing_sizes', '__return_true' );
+
+		$this->assertStringContainsString( 'sizes="(max-width: 480px) 300px"', $result );
+		$this->assertStringNotContainsString( '(max-width: 320px) 200px', $result );
+	}
+
+	/**
+	 * A filter returning false overrides the attribute, so the existing sizes are enhanced again.
+	 */
+	public function test_keep_existing_sizes_filter_can_override_attribute() {
+		$tag_replacer = new Optml_Tag_Replacer();
+
+		$tag = '<img src="https://example.com/image.jpg" srcset="existing-300w.jpg 300w" sizes="(max-width: 480px) 300px" data-optml-keep-sizes alt="Test" />';
+		$missing_srcsets = [
+			[ 'w' => 200, 'h' => 150, 'd' => 1, 's' => '200w', 'b' => 320 ],
+		];
+
+		$kept = $tag_replacer->add_missing_srcset_attributes( $tag, $missing_srcsets, 'https://example.com/image.jpg', false );
+		$this->assertStringNotContainsString( '(max-width: 320px) 200px', $kept );
+
+		add_filter( 'optml_keep_existing_sizes', '__return_false' );
+		$result = $tag_replacer->add_missing_srcset_attributes( $tag, $missing_srcsets, 'https://example.com/image.jpg', false );
+		remove_filter( 'optml_keep_existing_sizes', '__return_false' );
+
+		$this->assertStringContainsString( '(max-width: 320px) 200px', $result );
+	}
+
 	/**
 	 * Test retina images setting respect
 	 */