diff --git a/wp-includes/general-template.php b/wp-includes/general-template.php
index 5bed9212b..6224ce0b8 100644
--- a/wp-includes/general-template.php
+++ b/wp-includes/general-template.php
@@ -1114,20 +1114,20 @@ function get_calendar($initial = true, $echo = true) {
 	}
 
 	$unixmonth = mktime(0, 0 , 0, $thismonth, 1, $thisyear);
+	$last_day = date('t', $unixmonth);
 
 	// Get the next and previous month and year with at least one post
-	$previous = $wpdb->get_row("SELECT DISTINCT MONTH(post_date) AS month, YEAR(post_date) AS year
+	$previous = $wpdb->get_row("SELECT MONTH(post_date) AS month, YEAR(post_date) AS year
 		FROM $wpdb->posts
 		WHERE post_date < '$thisyear-$thismonth-01'
 		AND post_type = 'post' AND post_status = 'publish'
 			ORDER BY post_date DESC
 			LIMIT 1");
-	$next = $wpdb->get_row("SELECT	DISTINCT MONTH(post_date) AS month, YEAR(post_date) AS year
+	$next = $wpdb->get_row("SELECT MONTH(post_date) AS month, YEAR(post_date) AS year
 		FROM $wpdb->posts
-		WHERE post_date >	'$thisyear-$thismonth-01'
-		AND MONTH( post_date ) != MONTH( '$thisyear-$thismonth-01' )
+		WHERE post_date > '$thisyear-$thismonth-{$last_day} 23:59:59'
 		AND post_type = 'post' AND post_status = 'publish'
-			ORDER	BY post_date ASC
+			ORDER BY post_date ASC
 			LIMIT 1");
 
 	/* translators: Calendar caption: 1: month name, 2: 4-digit year */
@@ -1179,10 +1179,9 @@ function get_calendar($initial = true, $echo = true) {
 
 	// Get days with posts
 	$dayswithposts = $wpdb->get_results("SELECT DISTINCT DAYOFMONTH(post_date)
-		FROM $wpdb->posts WHERE MONTH(post_date) = '$thismonth'
-		AND YEAR(post_date) = '$thisyear'
+		FROM $wpdb->posts WHERE post_date >= '{$thisyear}-{$thismonth}-01 00:00:00'
 		AND post_type = 'post' AND post_status = 'publish'
-		AND post_date < '" . current_time('mysql') . '\'', ARRAY_N);
+		AND post_date <= '{$thisyear}-{$thismonth}-{$last_day} 23:59:59'", ARRAY_N);
 	if ( $dayswithposts ) {
 		foreach ( (array) $dayswithposts as $daywith ) {
 			$daywithpost[] = $daywith[0];
@@ -1199,9 +1198,8 @@ function get_calendar($initial = true, $echo = true) {
 	$ak_titles_for_day = array();
 	$ak_post_titles = $wpdb->get_results("SELECT ID, post_title, DAYOFMONTH(post_date) as dom "
 		."FROM $wpdb->posts "
-		."WHERE YEAR(post_date) = '$thisyear' "
-		."AND MONTH(post_date) = '$thismonth' "
-		."AND post_date < '".current_time('mysql')."' "
+		."WHERE post_date >= '{$thisyear}-{$thismonth}-01 00:00:00' "
+		."AND post_date <= '{$thisyear}-{$thismonth}-{$last_day} 23:59:59' "
 		."AND post_type = 'post' AND post_status = 'publish'"
 	);
 	if ( $ak_post_titles ) {