diff --git a/wp-includes/post.php b/wp-includes/post.php
index 0c462d28e5..180513f254 100644
--- a/wp-includes/post.php
+++ b/wp-includes/post.php
@@ -3790,6 +3790,27 @@ function wp_unique_post_slug( $slug, $post_ID, $post_status, $post_type, $post_p
 		$check_sql = "SELECT post_name FROM $wpdb->posts WHERE post_name = %s AND post_type = %s AND ID != %d LIMIT 1";
 		$post_name_check = $wpdb->get_var( $wpdb->prepare( $check_sql, $slug, $post_type, $post_ID ) );
 
+		// Prevent post slugs that could result in URLs that conflict with date archives.
+		$conflicts_with_date_archive = false;
+		if ( 'post' === $post_type && preg_match( '/^[0-9]+$/', $slug ) && $slug_num = intval( $slug ) ) {
+			$permastructs   = array_values( array_filter( explode( '/', get_option( 'permalink_structure' ) ) ) );
+			$postname_index = array_search( '%postname%', $permastructs );
+
+			/*
+			 * Potential date clashes are as follows:
+			 *
+			 * - Any integer in the first permastruct position could be a year.
+			 * - An integer between 1 and 12 that follows 'year' conflicts with 'monthnum'.
+			 * - An integer between 1 and 31 that follows 'monthnum' conflicts with 'day'.
+			 */
+			if ( 0 === $postname_index ||
+				( $postname_index && '%year%' === $permastructs[ $postname_index - 1 ] && 13 > $slug_num ) ||
+				( $postname_index && '%monthnum%' === $permastructs[ $postname_index - 1 ] && 32 > $slug_num )
+			) {
+				$conflicts_with_date_archive = true;
+			}
+		}
+
 		/**
 		 * Filter whether the post slug would be bad as a flat slug.
 		 *
@@ -3799,7 +3820,7 @@ function wp_unique_post_slug( $slug, $post_ID, $post_status, $post_type, $post_p
 		 * @param string $slug      The post slug.
 		 * @param string $post_type Post type.
 		 */
-		if ( $post_name_check || in_array( $slug, $feeds ) || apply_filters( 'wp_unique_post_slug_is_bad_flat_slug', false, $slug, $post_type ) ) {
+		if ( $post_name_check || in_array( $slug, $feeds ) || $conflicts_with_date_archive || apply_filters( 'wp_unique_post_slug_is_bad_flat_slug', false, $slug, $post_type ) ) {
 			$suffix = 2;
 			do {
 				$alt_post_name = _truncate_post_slug( $slug, 200 - ( strlen( $suffix ) + 1 ) ) . "-$suffix";
diff --git a/wp-includes/version.php b/wp-includes/version.php
index a7d39432b5..2b8bc4cf62 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.3-alpha-32646';
+$wp_version = '4.3-alpha-32647';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.