diff --git a/includes/options/class-amp-options-manager.php b/includes/options/class-amp-options-manager.php
index bbfbbb76f47..8f3adc564b6 100644
--- a/includes/options/class-amp-options-manager.php
+++ b/includes/options/class-amp-options-manager.php
@@ -718,23 +718,9 @@ public static function handle_updated_theme_support_option() {
 			$validation = AMP_Validation_Manager::validate_url( $url );
 
 			if ( is_wp_error( $validation ) ) {
-				$review_messages[] = esc_html(
-					sprintf(
-						/* translators: 1: error message. 2: error code. */
-						__( 'However, there was an error when checking the AMP validity for your site.', 'amp' ),
-						$validation->get_error_message(),
-						$validation->get_error_code()
-					)
-				);
-
-				$error_message = $validation->get_error_message();
-				if ( $error_message ) {
-					$review_messages[] = $error_message;
-				} else {
-					/* translators: %s is the error code */
-					$review_messages[] = esc_html( sprintf( __( 'Error code: %s.', 'amp' ), $validation->get_error_code() ) );
-				}
-				$notice_type = 'error';
+				$review_messages[] = esc_html__( 'However, there was an error when checking the AMP validity for your site.', 'amp' );
+				$review_messages[] = AMP_Validation_Manager::get_validate_url_error_message( $validation->get_error_code(), $validation->get_error_message() );
+				$notice_type       = 'error';
 			} elseif ( is_array( $validation ) ) {
 				$new_errors      = 0;
 				$rejected_errors = 0;
@@ -757,7 +743,7 @@ public static function handle_updated_theme_support_option() {
 				if ( $rejected_errors > 0 ) {
 					$notice_type = 'error';
 
-					$message = wp_kses_post(
+					$message = esc_html(
 						sprintf(
 							/* translators: %s is count of rejected errors */
 							_n(
@@ -772,43 +758,37 @@ public static function handle_updated_theme_support_option() {
 					);
 
 					if ( $invalid_url_screen_url ) {
-						$message .= ' ' . wp_kses_post(
-							sprintf(
-								/* translators: %s is URL to review issues */
-								_n(
-									'<a href="%s">Review Issue</a>.',
-									'<a href="%s">Review Issues</a>.',
-									$rejected_errors,
-									'amp'
-								),
-								esc_url( $invalid_url_screen_url )
-							)
+						$message .= ' ' . sprintf(
+							/* translators: %s is URL to review issues */
+							_n(
+								'<a href="%s">Review Issue</a>.',
+								'<a href="%s">Review Issues</a>.',
+								$rejected_errors,
+								'amp'
+							),
+							esc_url( $invalid_url_screen_url )
 						);
 					}
 
 					$review_messages[] = $message;
 				} else {
-					$message = wp_kses_post(
-						sprintf(
-							/* translators: %s is an AMP URL */
-							__( 'View an <a href="%s">AMP version of your site</a>.', 'amp' ),
-							esc_url( $url )
-						)
+					$message = sprintf(
+						/* translators: %s is an AMP URL */
+						__( 'View an <a href="%s">AMP version of your site</a>.', 'amp' ),
+						esc_url( $url )
 					);
 
 					if ( $new_errors > 0 && $invalid_url_screen_url ) {
-						$message .= ' ' . wp_kses_post(
-							sprintf(
-								/* translators: 1: URL to review issues. 2: count of new errors. */
-								_n(
-									'Please also <a href="%1$s">review %2$s issue</a> which may need to be fixed (for one URL at least).',
-									'Please also <a href="%1$s">review %2$s issues</a> which may need to be fixed (for one URL at least).',
-									$new_errors,
-									'amp'
-								),
-								esc_url( $invalid_url_screen_url ),
-								number_format_i18n( $new_errors )
-							)
+						$message .= ' ' . sprintf(
+							/* translators: 1: URL to review issues. 2: count of new errors. */
+							_n(
+								'Please also <a href="%1$s">review %2$s issue</a> which may need to be fixed (for one URL at least).',
+								'Please also <a href="%1$s">review %2$s issues</a> which may need to be fixed (for one URL at least).',
+								$new_errors,
+								'amp'
+							),
+							esc_url( $invalid_url_screen_url ),
+							number_format_i18n( $new_errors )
 						);
 					}
 
@@ -831,18 +811,16 @@ public static function handle_updated_theme_support_option() {
 				}
 				break;
 			case AMP_Theme_Support::READER_MODE_SLUG:
-				$message = wp_kses_post(
-					sprintf(
-						/* translators: %s is an AMP URL */
-						__( 'Reader mode activated! View the <a href="%s">AMP version of a recent post</a>. It is recommended that you upgrade to Standard or Transitional mode.', 'amp' ),
-						esc_url( $url )
-					)
+				$message = sprintf(
+					/* translators: %s is an AMP URL */
+					__( 'Reader mode activated! View the <a href="%s">AMP version of a recent post</a>. It is recommended that you upgrade to Standard or Transitional mode.', 'amp' ),
+					esc_url( $url )
 				);
 				break;
 		}
 
 		if ( isset( $message ) ) {
-			add_settings_error( self::OPTION_NAME, 'template_mode_updated', $message, $notice_type );
+			add_settings_error( self::OPTION_NAME, 'template_mode_updated', wp_kses_post( $message ), $notice_type );
 		}
 	}
 }
diff --git a/includes/validation/class-amp-validated-url-post-type.php b/includes/validation/class-amp-validated-url-post-type.php
index 5e0c925dfa6..c752e49444a 100644
--- a/includes/validation/class-amp-validated-url-post-type.php
+++ b/includes/validation/class-amp-validated-url-post-type.php
@@ -631,17 +631,13 @@ public static function get_url_from_post( $post ) {
 	/**
 	 * Normalize a URL for storage.
 	 *
-	 * This ensures that query vars like utm_* and the like will not cause duplicates.
 	 * The AMP query param is removed to facilitate switching between standard and transitional.
 	 * The URL scheme is also normalized to HTTPS to help with transition from HTTP to HTTPS.
 	 *
 	 * @param string $url URL.
 	 * @return string Normalized URL.
-	 * @global WP $wp
 	 */
 	protected static function normalize_url_for_storage( $url ) {
-		global $wp;
-
 		// Only ever store the canonical version.
 		$url = amp_remove_endpoint( $url );
 
@@ -651,12 +647,11 @@ protected static function normalize_url_for_storage( $url ) {
 		// Normalize query args, removing all that are not recognized or which are removable.
 		$url_parts = explode( '?', $url, 2 );
 		if ( 2 === count( $url_parts ) ) {
-			parse_str( $url_parts[1], $args );
+			$args = wp_parse_args( $url_parts[1] );
 			foreach ( wp_removable_query_args() as $removable_query_arg ) {
 				unset( $args[ $removable_query_arg ] );
 			}
-			$args = wp_array_slice_assoc( $args, $wp->public_query_vars );
-			$url  = $url_parts[0];
+			$url = $url_parts[0];
 			if ( ! empty( $args ) ) {
 				$url = $url_parts[0] . '?' . build_query( $args );
 			}
@@ -1231,7 +1226,7 @@ public static function handle_bulk_action( $redirect, $action, $items ) {
 
 			$validity = AMP_Validation_Manager::validate_url( $url );
 			if ( is_wp_error( $validity ) ) {
-				$errors[] = $validity->get_error_code();
+				$errors[] = AMP_Validation_Manager::get_validate_url_error_message( $validity->get_error_code(), $validity->get_error_message() );
 				continue;
 			}
 
@@ -1259,13 +1254,13 @@ static function( $error ) {
 			self::URLS_TESTED => count( $items ),
 		];
 		if ( ! empty( $errors ) ) {
-			$args['amp_validate_error'] = $errors;
+			$args['amp_validate_error'] = AMP_Validation_Manager::serialize_validation_error_messages( $errors );
 		} else {
 			$args[ self::REMAINING_ERRORS ] = count( $remaining_invalid_urls );
 		}
 
 		$redirect = remove_query_arg( wp_removable_query_args(), $redirect );
-		return add_query_arg( $args, $redirect );
+		return add_query_arg( rawurlencode_deep( $args ), $redirect );
 	}
 
 	/**
@@ -1278,14 +1273,23 @@ public static function print_admin_notice() {
 			return;
 		}
 
-		if ( isset( $_GET['amp_validate_error'] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Recommended
-			$error_codes = array_unique( array_map( 'sanitize_key', (array) $_GET['amp_validate_error'] ) ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended
-			foreach ( $error_codes as $error_code ) {
-				printf(
-					'<div class="notice is-dismissible error"><p>%s</p><button type="button" class="notice-dismiss"><span class="screen-reader-text">%s</span></button></div>',
-					esc_html( AMP_Validation_Manager::get_validate_url_error_message( $error_code ) ),
-					esc_html__( 'Dismiss this notice.', 'amp' )
-				);
+		if ( isset( $_GET['amp_validate_error'] ) && is_string( $_GET['amp_validate_error'] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Recommended
+			// Note: The input var is validated by the unserialize_validation_error_messages method.
+			$errors = AMP_Validation_Manager::unserialize_validation_error_messages( wp_unslash( $_GET['amp_validate_error'] ) ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended
+			if ( $errors ) {
+				foreach ( array_unique( $errors ) as $error_message ) {
+					printf(
+						'<div class="notice is-dismissible error"><p>%s</p><button type="button" class="notice-dismiss"><span class="screen-reader-text">%s</span></button></div>',
+						wp_kses(
+							$error_message,
+							[
+								'a'    => array_fill_keys( [ 'href', 'target' ], true ),
+								'code' => [],
+							]
+						),
+						esc_html__( 'Dismiss this notice.', 'amp' )
+					);
+				}
 			}
 		}
 
@@ -1487,7 +1491,7 @@ public static function handle_validate_request() {
 
 			$validity = AMP_Validation_Manager::validate_url( $url );
 			if ( is_wp_error( $validity ) ) {
-				throw new Exception( esc_html( $validity->get_error_code() ) );
+				throw new Exception( AMP_Validation_Manager::get_validate_url_error_message( $validity->get_error_code(), $validity->get_error_message() ) );
 			}
 
 			$errors = wp_list_pluck( $validity['results'], 'error' );
@@ -1502,7 +1506,7 @@ public static function handle_validate_request() {
 				)
 			);
 			if ( is_wp_error( $stored ) ) {
-				throw new Exception( esc_html( $stored->get_error_code() ) );
+				throw new Exception( AMP_Validation_Manager::get_validate_url_error_message( $stored->get_error_code(), $stored->get_error_message() ) );
 			}
 			$redirect = get_edit_post_link( $stored, 'raw' );
 
@@ -1518,7 +1522,9 @@ static function ( $error ) {
 			$args[ self::URLS_TESTED ]      = '1';
 			$args[ self::REMAINING_ERRORS ] = $error_count;
 		} catch ( Exception $e ) {
-			$args['amp_validate_error'] = $e->getMessage();
+			$args['amp_validate_error'] = AMP_Validation_Manager::serialize_validation_error_messages(
+				[ $e->getMessage() ]
+			);
 			$args[ self::URLS_TESTED ]  = '0';
 
 			if ( $post && self::POST_TYPE_SLUG === $post->post_type ) {
@@ -1533,7 +1539,7 @@ static function ( $error ) {
 			}
 		}
 
-		wp_safe_redirect( add_query_arg( $args, $redirect ) );
+		wp_safe_redirect( add_query_arg( rawurlencode_deep( $args ), $redirect ) );
 		exit();
 	}
 
@@ -2073,7 +2079,7 @@ public static function get_recheck_url( $url_or_post ) {
 		}
 
 		return wp_nonce_url(
-			add_query_arg( $args, admin_url() ),
+			add_query_arg( rawurlencode_deep( $args ), admin_url() ),
 			self::NONCE_ACTION
 		);
 	}
diff --git a/includes/validation/class-amp-validation-manager.php b/includes/validation/class-amp-validation-manager.php
index a5d74659708..25f9aa93eb5 100644
--- a/includes/validation/class-amp-validation-manager.php
+++ b/includes/validation/class-amp-validation-manager.php
@@ -1874,17 +1874,14 @@ public static function validate_url( $url ) {
 
 		$response = wp_remote_retrieve_body( $r );
 		if ( trim( $response ) === '' ) {
-			$error_code = 'white_screen_of_death';
-			return new WP_Error( $error_code, self::get_validate_url_error_message( $error_code ) );
+			return new WP_Error( 'white_screen_of_death' );
 		}
 		if ( ! preg_match( '#</body>.*?<!--\s*AMP_VALIDATION\s*:\s*(\{.*?\})\s*-->#s', $response, $matches ) ) {
-			$error_code = 'response_comment_absent';
-			return new WP_Error( $error_code, self::get_validate_url_error_message( $error_code ) );
+			return new WP_Error( 'response_comment_absent' );
 		}
 		$validation = json_decode( $matches[1], true );
 		if ( json_last_error() || ! isset( $validation['results'] ) || ! is_array( $validation['results'] ) ) {
-			$error_code = 'malformed_json_validation_errors';
-			return new WP_Error( $error_code, self::get_validate_url_error_message( $error_code ) );
+			return new WP_Error( 'malformed_json_validation_errors' );
 		}
 
 		return array_merge(
@@ -1893,38 +1890,105 @@ public static function validate_url( $url ) {
 		);
 	}
 
+	/**
+	 * Serialize validation error messages.
+	 *
+	 * In order to safely pass validation error messages through redirects with query parameters, they must be serialized
+	 * with a HMAC for security. The messages contain markup so the HMAC prevents tampering.
+	 *
+	 * @since 1.4.2
+	 * @see AMP_Validation_Manager::unserialize_validation_error_messages()
+	 *
+	 * @param string[] $messages Messages.
+	 * @return string Serialized.
+	 */
+	public static function serialize_validation_error_messages( $messages ) {
+		$encoded_messages = base64_encode( wp_json_encode( array_unique( $messages ) ) ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_encode
+		return wp_hash( $encoded_messages ) . ':' . $encoded_messages;
+	}
+
+	/**
+	 * Unserialize validation error messages.
+	 *
+	 * @since 1.4.2
+	 * @see AMP_Validation_Manager::serialize_validation_error_messages()
+	 *
+	 * @param string $serialized Serialized messages.
+	 * @return string[]|null
+	 */
+	public static function unserialize_validation_error_messages( $serialized ) {
+		$parts = explode( ':', $serialized, 2 );
+		if ( count( $parts ) !== 2 || wp_hash( $parts[1] ) !== $parts[0] ) {
+			return null;
+		}
+		return json_decode( base64_decode( $parts[1] ), true ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_decode
+	}
+
 	/**
 	 * Get error message for a validate URL failure.
 	 *
-	 * @param string $error_code Error code.
-	 * @return string Error message.
+	 * @param string $error_code    Error code.
+	 * @param string $error_message Error message, typically technical such as from HTTP status text or cURL error message.
+	 * @return string Error message with HTML markup.
 	 */
-	public static function get_validate_url_error_message( $error_code ) {
-		$check_error_log = __( 'Please check your server\'s PHP error logs; to do this you may need to enable WP_DEBUG_LOG.', 'amp' );
+	public static function get_validate_url_error_message( $error_code, $error_message = '' ) {
+		$check_error_log = sprintf(
+			/* translators: %s is link to Debugging in WordPress */
+			' ' . __( 'Please check your server PHP error logs; to do this you may need to <a href="%s" target="_blank">enable</a> <code>WP_DEBUG_LOG</code>.', 'amp' ),
+			esc_url( 'https://wordpress.org/support/article/debugging-in-wordpress/' )
+		);
+
+		if ( $error_message ) {
+			$error_message = ' ' . rtrim( $error_message, '.' ) . '.';
+		}
+
+		$support_forum_message = ' ' . sprintf(
+			/* translators: %1$s: Link to support forum. %2$s: Link to new topic form in support forum. */
+			__( 'If you are stuck, please search the <a href="%1$s">support forum</a> for possible related topics, or otherwise start a <a href="%2$s">new support topic</a> including the error message, the URL to your site, and your active theme/plugins.', 'amp' ),
+			esc_url( 'https://wordpress.org/support/plugin/amp/' ),
+			esc_url( 'https://wordpress.org/support/plugin/amp/#new-topic-0' )
+		);
+
+		$site_health_message = '';
+		if ( version_compare( get_bloginfo( 'version' ), '5.2', '>=' ) ) {
+			$site_health_message .= ' ' . sprintf(
+				/* translators: %s is link to Site Health */
+				__( 'Please check your <a href="%s">Site Health</a> to verify it can perform loopback requests.', 'amp' ),
+				esc_url( admin_url( 'site-health.php' ) )
+			);
+			$support_forum_message .= ' ' . sprintf(
+				/* translators: %s is the URL to Site Health Info. */
+				__( 'Please include your <a href="%s">Site Health Info</a>.', 'amp' ),
+				esc_url( admin_url( 'site-health.php?tab=debug' ) )
+			);
+		}
+
 		switch ( $error_code ) {
 			case 'http_request_failed':
-				return __( 'Failed to fetch URL(s) to validate. This may be due to a request timeout.', 'amp' ) . ' ' . $check_error_log;
+				return __( 'Failed to fetch URL to validate.', 'amp' ) . $error_message . $site_health_message . $support_forum_message;
 			case 'white_screen_of_death':
-				return __( 'Unable to validate URL. Encountered a white screen of death likely due to a fatal error.', 'amp' ) . ' ' . $check_error_log;
+				return __( 'Unable to validate URL. Encountered a white screen of death likely due to a PHP fatal error.', 'amp' ) . $error_message . $check_error_log . $support_forum_message;
 			case '404':
-				return __( 'The fetched URL was not found. It may have been deleted. If so, you can trash this.', 'amp' );
+				return __( 'The fetched URL was not found. It may have been deleted. If so, you can trash this.', 'amp' ) . $error_message . $support_forum_message;
 			case '500':
-				return __( 'An internal server error occurred when fetching the URL for validation.', 'amp' ) . ' ' . $check_error_log;
+				return __( 'An internal server error occurred when fetching the URL for validation.', 'amp' ) . $error_message . $check_error_log . $support_forum_message;
 			case 'response_comment_absent':
 				return sprintf(
-					/* translators: %s: AMP_VALIDATION */
-					__( 'URL validation failed to due to the absence of the expected JSON-containing %s comment after the body. This is often due to a PHP fatal error occurring.', 'amp' ),
-					'AMP_VALIDATION'
-				) . ' ' . $check_error_log;
+					/* translators: %1$s: AMP_VALIDATION, %2$s: </body> */
+					__( 'URL validation failed to due to the absence of the expected JSON-containing %1$s HTML comment after %2$s. This is often due to a PHP fatal error occurring.', 'amp' ),
+					'<code>AMP_VALIDATION</code>',
+					'<code>&lt;/body&gt;</code>'
+				) . $error_message . $check_error_log . $support_forum_message;
 			case 'malformed_json_validation_errors':
 				return sprintf(
-					/* translators: %s: AMP_VALIDATION */
-					__( 'URL validation failed to due to unexpected JSON in the %s comment after the body.', 'amp' ),
-					'AMP_VALIDATION'
-				);
+					/* translators: %1$s: AMP_VALIDATION, %2$s: </body> */
+					__( 'URL validation failed to due to unexpected JSON in the %1$s HTML comment after %2$s.', 'amp' ),
+					'<code>AMP_VALIDATION</code>',
+					'<code>&lt;/body&gt;</code>'
+				) . $error_message . $support_forum_message;
 			default:
 				/* translators: %s is error code */
-				return sprintf( __( 'URL validation failed. Error code: %s.', 'amp' ), $error_code ); // Note that $error_code has been sanitized with sanitize_key(); will be escaped below as well.
+				return sprintf( __( 'URL validation failed. Error code: %s.', 'amp' ), $error_code ) . $error_message . $support_forum_message;
 		}
 	}
 
diff --git a/tests/php/validation/test-class-amp-validated-url-post-type.php b/tests/php/validation/test-class-amp-validated-url-post-type.php
index 024bbe06c9b..8a7478918d0 100644
--- a/tests/php/validation/test-class-amp-validated-url-post-type.php
+++ b/tests/php/validation/test-class-amp-validated-url-post-type.php
@@ -265,7 +265,10 @@ public function test_get_invalid_url_post() {
 
 		// Test normalized.
 		$args = [ 'normalize' => false ];
-		$url  = add_query_arg( 'utm_foo', 'bar', get_permalink( $post ) . '#baz' );
+		$url  = add_query_arg(
+			array_fill_keys( wp_removable_query_args(), 'true' ),
+			get_permalink( $post ) . '#baz'
+		);
 		$url  = set_url_scheme( $url, 'http' );
 		$this->assertNull( AMP_Validated_URL_Post_Type::get_invalid_url_post( $url, $args ) );
 		$args = [ 'normalize' => true ];
@@ -805,14 +808,8 @@ static function() {
 				];
 			}
 		);
-		$this->assertEquals(
-			add_query_arg(
-				[
-					AMP_Validated_URL_Post_Type::URLS_TESTED => $urls_tested,
-					'amp_validate_error' => [ 'response_comment_absent' ],
-				],
-				$initial_redirect
-			),
+		$this->assertContains(
+			'amp_validate_error=',
 			AMP_Validated_URL_Post_Type::handle_bulk_action( $initial_redirect, AMP_Validated_URL_Post_Type::BULK_VALIDATE_ACTION, $items )
 		);
 	}
@@ -821,6 +818,8 @@ static function() {
 	 * Test for print_admin_notice()
 	 *
 	 * @covers \AMP_Validated_URL_Post_Type::print_admin_notice()
+	 * @covers \AMP_Validation_Manager::serialize_validation_error_messages()
+	 * @covers \AMP_Validation_Manager::unserialize_validation_error_messages()
 	 */
 	public function test_print_admin_notice() {
 		add_theme_support( AMP_Theme_Support::SLUG );
@@ -853,9 +852,10 @@ public function test_print_admin_notice() {
 		$output = get_echo( [ 'AMP_Validated_URL_Post_Type', 'print_admin_notice' ] );
 		$this->assertContains( 'The rechecked URL is free of non-removed invalid markup.', $output );
 
-		$_GET['amp_validate_error'] = [ 'http_request_failed' ];
+		$error_message              = 'Something <code>bad</code> happened!';
+		$_GET['amp_validate_error'] = AMP_Validation_Manager::serialize_validation_error_messages( [ $error_message ] );
 		$output                     = get_echo( [ 'AMP_Validated_URL_Post_Type', 'print_admin_notice' ] );
-		$this->assertContains( 'Failed to fetch URL(s) to validate', $output );
+		$this->assertContains( $error_message, $output );
 
 		unset( $GLOBALS['current_screen'] );
 	}
@@ -926,8 +926,8 @@ static function( $error ) {
 		$exception = $handle_validate_request();
 		$this->assertInstanceOf( 'Exception', $exception );
 		$this->assertEquals( 302, $exception->getCode() );
-		$this->assertStringEndsWith(
-			'/edit.php?post_type=amp_validated_url&amp_validate_error=missing_url&amp_urls_tested=0',
+		$this->assertContains(
+			'/edit.php?post_type=amp_validated_url&amp_validate_error=',
 			$exception->getMessage()
 		);
 		unset( $_GET['post'] ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended
@@ -937,8 +937,8 @@ static function( $error ) {
 		$exception    = $handle_validate_request();
 		$this->assertInstanceOf( 'Exception', $exception );
 		$this->assertEquals( 302, $exception->getCode() );
-		$this->assertStringEndsWith(
-			'/edit.php?post_type=amp_validated_url&amp_validate_error=invalid_post&amp_urls_tested=0',
+		$this->assertContains(
+			'/edit.php?post_type=amp_validated_url&amp_validate_error=',
 			$exception->getMessage()
 		);
 		unset( $_GET['post'] ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended
@@ -948,8 +948,8 @@ static function( $error ) {
 		$exception    = $handle_validate_request();
 		$this->assertInstanceOf( 'Exception', $exception );
 		$this->assertEquals( 302, $exception->getCode() );
-		$this->assertStringEndsWith(
-			'/edit.php?post_type=amp_validated_url&amp_validate_error=invalid_post&amp_urls_tested=0',
+		$this->assertContains(
+			'/edit.php?post_type=amp_validated_url&amp_validate_error=',
 			$exception->getMessage()
 		);
 		unset( $_GET['post'] ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended
@@ -959,8 +959,8 @@ static function( $error ) {
 		$exception    = $handle_validate_request();
 		$this->assertInstanceOf( 'Exception', $exception );
 		$this->assertEquals( 302, $exception->getCode() );
-		$this->assertStringEndsWith(
-			sprintf( 'post.php?post=%s&action=edit&amp_urls_tested=1&amp_remaining_errors=2', $post_id ),
+		$this->assertContains(
+			sprintf( 'post.php?post=%s&action=edit&amp_urls_tested=', $post_id ),
 			$exception->getMessage()
 		);
 		unset( $_GET['post'] ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended
@@ -990,8 +990,8 @@ static function( $error ) {
 		$exception   = $handle_validate_request();
 		$this->assertInstanceOf( 'Exception', $exception );
 		$this->assertEquals( 302, $exception->getCode() );
-		$this->assertStringEndsWith(
-			'wp-admin/edit.php?post_type=amp_validated_url&amp_validate_error=illegal_url&amp_urls_tested=0',
+		$this->assertContains(
+			'wp-admin/edit.php?post_type=amp_validated_url&amp_validate_error=',
 			$exception->getMessage()
 		);
 	}