diff --git a/.github/workflows/build-test-measure.yml b/.github/workflows/build-test-measure.yml
index a4801f98023..facc17fcb1e 100644
--- a/.github/workflows/build-test-measure.yml
+++ b/.github/workflows/build-test-measure.yml
@@ -328,11 +328,11 @@ jobs:
             external-http: true
 
           - php: '7.4'
-            wp: '6.3'
+            wp: '6.5'
             phpunit: '7'
 
           - php: '7.4'
-            wp: '6.3'
+            wp: '6.5'
             phpunit: '7'
             external-http: true
     steps:
@@ -507,7 +507,7 @@ jobs:
             wp: 'latest'
 
           - php: '7.4'
-            wp: '6.3'
+            wp: '6.5'
     steps:
       - name: Shutdown default MySQL service
         if: needs.pre-run.outputs.changed-php-count > 0
diff --git a/README.md b/README.md
index 3f4a2104b09..8c7d22253c6 100644
--- a/README.md
+++ b/README.md
@@ -6,7 +6,7 @@ An easier path to great Page Experience for everyone. Powered by AMP.
 
 **Contributors:** [google](https://profiles.wordpress.org/google), [xwp](https://profiles.wordpress.org/xwp), [rtcamp](https://profiles.wordpress.org/rtcamp), [automattic](https://profiles.wordpress.org/automattic), [westonruter](https://profiles.wordpress.org/westonruter), [albertomedina](https://profiles.wordpress.org/albertomedina), [schlessera](https://profiles.wordpress.org/schlessera), [delawski](https://profiles.wordpress.org/delawski/), [swissspidy](https://profiles.wordpress.org/swissspidy), [pierlo](https://profiles.wordpress.org/pierlo), [joshuawold](https://profiles.wordpress.org/joshuawold), [thelovekesh](https://profiles.wordpress.org/thelovekesh/)  
 **Tags:** [page experience](https://wordpress.org/plugins/tags/page-experience), [performance](https://wordpress.org/plugins/tags/performance), [amp](https://wordpress.org/plugins/tags/amp), [mobile](https://wordpress.org/plugins/tags/mobile), [optimization](https://wordpress.org/plugins/tags/optimization)  
-**Requires at least:** 6.3  
+**Requires at least:** 6.5  
 **Tested up to:** 6.6  
 **Stable tag:** 2.5.4  
 **License:** [GPLv2 or later](http://www.gnu.org/licenses/gpl-2.0.html)  
diff --git a/amp.php b/amp.php
index a34c60fdd39..1dcb030db88 100644
--- a/amp.php
+++ b/amp.php
@@ -7,7 +7,7 @@
  * Author URI: https://github.com/ampproject/amp-wp/graphs/contributors
  * Version: 2.5.5-alpha
  * License: GPLv2 or later
- * Requires at least: 6.3
+ * Requires at least: 6.5
  * Requires PHP: 7.4
  *
  * @package AMP
diff --git a/includes/validation/class-amp-validation-manager.php b/includes/validation/class-amp-validation-manager.php
index 1d4ba232b1d..cac607113e8 100644
--- a/includes/validation/class-amp-validation-manager.php
+++ b/includes/validation/class-amp-validation-manager.php
@@ -1166,7 +1166,7 @@ static function ( $enqueued_script_source ) use ( $script_handle ) {
 
 						$has_non_core = false;
 						foreach ( $extra_sources as $extra_source ) {
-							if ( 'core' !== $extra_source['type'] ) {
+							if ( isset( $extra_source['type'] ) && 'core' !== $extra_source['type'] ) {
 								$has_non_core = true;
 								break;
 							}
diff --git a/src/DependencySupport.php b/src/DependencySupport.php
index d58511c571e..31b51953744 100644
--- a/src/DependencySupport.php
+++ b/src/DependencySupport.php
@@ -30,7 +30,7 @@ class DependencySupport implements Service {
 	 *
 	 * @var string
 	 */
-	const WP_MIN_VERSION = '6.3';
+	const WP_MIN_VERSION = '6.5';
 
 	/**
 	 * Determines whether core or Gutenberg provides minimal support.
diff --git a/tests/php/src/Admin/AmpPluginsTest.php b/tests/php/src/Admin/AmpPluginsTest.php
index 511a20997f3..507eea3692b 100644
--- a/tests/php/src/Admin/AmpPluginsTest.php
+++ b/tests/php/src/Admin/AmpPluginsTest.php
@@ -161,7 +161,7 @@ public function test_is_needed() {
 		$this->assertFalse( AmpPlugins::is_needed() );
 
 		// Test 3: Admin request in supported WordPress .
-		$wp_version = '6.3';
+		$wp_version = '6.5';
 		set_current_screen( 'index.php' );
 		$this->assertTrue( AmpPlugins::is_needed() );
 
diff --git a/tests/php/src/Admin/AmpThemesTest.php b/tests/php/src/Admin/AmpThemesTest.php
index 0b18aae8f8a..3c5bbbcda22 100644
--- a/tests/php/src/Admin/AmpThemesTest.php
+++ b/tests/php/src/Admin/AmpThemesTest.php
@@ -83,7 +83,7 @@ public function test_is_needed() {
 		$this->assertFalse( AmpThemes::is_needed() );
 
 		// Test 3: Admin request.
-		$wp_version = '6.3';
+		$wp_version = '6.5';
 		set_current_screen( 'index.php' );
 		$this->assertTrue( is_admin() );
 		$this->assertTrue( AmpThemes::is_needed() );
diff --git a/tests/php/test-amp-style-sanitizer.php b/tests/php/test-amp-style-sanitizer.php
index b2ee1a986e3..7142e5a8503 100644
--- a/tests/php/test-amp-style-sanitizer.php
+++ b/tests/php/test-amp-style-sanitizer.php
@@ -3524,11 +3524,11 @@ function ( $original_dom, $original_source, $amphtml_dom, $amphtml_source ) {
 						$this->assertStringContainsString( '.wp-block-audio figcaption', $amphtml_source, 'Expected block-library/style.css' );
 					}
 
-					if ( version_compare( strtok( get_bloginfo( 'version' ), '-' ), '6.6', '>=' ) ) {
-						$this->assertStringContainsString( '[class^="wp-block-"]:not(.wp-block-gallery) > figcaption', $amphtml_source, 'Expected twentyten/blocks.css' );
-					} else {
-						$this->assertStringContainsString( '[class^="wp-block-"]:not(.wp-block-gallery) figcaption', $amphtml_source, 'Expected twentyten/blocks.css' );
-					}
+					$this->assertStringContainsString(
+						'[class^="wp-block-"]:not(.wp-block-gallery) figcaption',
+						str_replace( '> figcaption', 'figcaption', $amphtml_source ),  // Account for recent CSS changes.
+						'Expected twentyten/blocks.css'
+					);
 
 					$amphtml_source = preg_replace( '/\s*>\s*/', '>', $amphtml_source ); // Account for variance in postcss.
 					$this->assertStringContainsString( '.amp-wp-default-form-message>p', $amphtml_source, 'Expected amp-default.css' );