diff --git a/src/wp-includes/wp-db.php b/src/wp-includes/wp-db.php
index d261254926..50d71c6c13 100644
--- a/src/wp-includes/wp-db.php
+++ b/src/wp-includes/wp-db.php
@@ -735,41 +735,62 @@ class wpdb {
 	 */
 	public function init_charset() {
 		if ( function_exists('is_multisite') && is_multisite() ) {
-			$this->charset = 'utf8';
+			$charset = 'utf8';
 			if ( defined( 'DB_COLLATE' ) && DB_COLLATE ) {
-				$this->collate = DB_COLLATE;
+				$collate = DB_COLLATE;
 			} else {
-				$this->collate = 'utf8_general_ci';
+				$collate = 'utf8_general_ci';
 			}
 		} elseif ( defined( 'DB_COLLATE' ) ) {
-			$this->collate = DB_COLLATE;
+			$collate = DB_COLLATE;
 		}
 
 		if ( defined( 'DB_CHARSET' ) ) {
-			$this->charset = DB_CHARSET;
+			$charset = DB_CHARSET;
 		}
 
+		$charset_collate = $this->determine_charset( $charset, $collate );
+
+		$this->charset = $charset_collate['charset'];
+		$this->collate = $charset_collate['collate'];
+	}
+
+	/**
+	 * Given a charset and collation, determine the best charset and collation to use.
+	 *
+	 * For example, when able, utf8mb4 should be used instead of utf8.
+	 *
+	 * @since 4.6.0
+	 *
+	 * @param  string $charset The character set to check.
+	 * @param  string $collate The collation to check.
+	 *
+	 * @return array The most appropriate character set and collation to use.
+	 */
+	public function determine_charset( $charset, $collate ) {
 		if ( ( $this->use_mysqli && ! ( $this->dbh instanceof mysqli ) ) || empty( $this->dbh ) ) {
-			return;
+			return compact( 'charset', 'collate' );
 		}
 
-		if ( 'utf8' === $this->charset && $this->has_cap( 'utf8mb4' ) ) {
-			$this->charset = 'utf8mb4';
+		if ( 'utf8' === $charset && $this->has_cap( 'utf8mb4' ) ) {
+			$charset = 'utf8mb4';
 		}
 
-		if ( 'utf8mb4' === $this->charset ) {
+		if ( 'utf8mb4' === $charset ) {
 			// _general_ is outdated, so we can upgrade it to _unicode_, instead.
-			if ( ! $this->collate || 'utf8_general_ci' === $this->collate ) {
-				$this->collate = 'utf8mb4_unicode_ci';
+			if ( ! $collate || 'utf8_general_ci' === $collate ) {
+				$collate = 'utf8mb4_unicode_ci';
 			} else {
-				$this->collate = str_replace( 'utf8_', 'utf8mb4_', $this->collate );
+				$collate = str_replace( 'utf8_', 'utf8mb4_', $collate );
 			}
 		}
 
 		// _unicode_520_ is a better collation, we should use that when it's available.
-		if ( $this->has_cap( 'utf8mb4_520' ) && 'utf8mb4_unicode_ci' === $this->collate ) {
-			$this->collate = 'utf8mb4_unicode_520_ci';
+		if ( $this->has_cap( 'utf8mb4_520' ) && 'utf8mb4_unicode_ci' === $collate ) {
+			$collate = 'utf8mb4_unicode_520_ci';
 		}
+
+		return compact( 'charset', 'collate' );
 	}
 
 	/**
diff --git a/tests/phpunit/tests/db.php b/tests/phpunit/tests/db.php
index f49a3e07b6..62077b0c12 100644
--- a/tests/phpunit/tests/db.php
+++ b/tests/phpunit/tests/db.php
@@ -955,4 +955,78 @@ class Tests_DB extends WP_UnitTestCase {
 
 		$wpdb->check_connection();
 	}
+
+	/**
+	 * @ticket 36917
+	 */
+	function test_charset_not_determined_when_disconnected() {
+		global $wpdb;
+
+		$charset = 'utf8';
+		$collate = 'this_isnt_a_collation';
+
+		$wpdb->close();
+
+		$result = $wpdb->determine_charset( $charset, $collate );
+
+		$this->assertSame( compact( 'charset', 'collate' ), $result );
+
+		$wpdb->check_connection();
+	}
+
+	/**
+	 * @ticket 36917
+	 */
+	function test_charset_switched_to_utf8mb4() {
+		global $wpdb;
+
+		if ( ! $wpdb->has_cap( 'utf8mb4' ) ) {
+			$this->markTestSkipped( 'This test requires utf8mb4 support.' );
+		}
+
+		$charset = 'utf8';
+		$collate = 'utf8_general_ci';
+
+		$result = $wpdb->determine_charset( $charset, $collate );
+
+		$this->assertSame( 'utf8mb4', $result['charset'] );
+	}
+
+	/**
+	 * @ticket 32105
+	 * @ticket 36917
+	 */
+	function test_collate_switched_to_utf8mb4_520() {
+		global $wpdb;
+
+		if ( ! $wpdb->has_cap( 'utf8mb4_520' ) ) {
+			$this->markTestSkipped( 'This test requires utf8mb4_520 support.' );
+		}
+
+		$charset = 'utf8';
+		$collate = 'utf8_general_ci';
+
+		$result = $wpdb->determine_charset( $charset, $collate );
+
+		$this->assertSame( 'utf8mb4_unicode_520_ci', $result['collate'] );
+	}
+
+	/**
+	 * @ticket 36917
+	 * @ticket 37522
+	 */
+	function test_non_unicode_collations() {
+		global $wpdb;
+
+		if ( ! $wpdb->has_cap( 'utf8mb4' ) ) {
+			$this->markTestSkipped( 'This test requires utf8mb4 support.' );
+		}
+
+		$charset = 'utf8';
+		$collate = 'utf8_swedish_ci';
+
+		$result = $wpdb->determine_charset( $charset, $collate );
+
+		$this->assertSame( 'utf8mb4_swedish_ci', $result['collate'] );
+	}
 }