diff --git a/src/wp-includes/wp-db.php b/src/wp-includes/wp-db.php
index f4f0826897..cc33b217a0 100644
--- a/src/wp-includes/wp-db.php
+++ b/src/wp-includes/wp-db.php
@@ -779,6 +779,11 @@ class wpdb {
 			$charset = 'utf8mb4';
 		}
 
+		if ( 'utf8mb4' === $charset && ! $this->has_cap( 'utf8mb4' ) ) {
+			$charset = 'utf8';
+			$collate = str_replace( 'utf8mb4_', 'utf8_', $collate );
+		}
+
 		if ( 'utf8mb4' === $charset ) {
 			// _general_ is outdated, so we can upgrade it to _unicode_, instead.
 			if ( ! $collate || 'utf8_general_ci' === $collate ) {
diff --git a/tests/phpunit/tests/db.php b/tests/phpunit/tests/db.php
index 7cff637149..0710965367 100644
--- a/tests/phpunit/tests/db.php
+++ b/tests/phpunit/tests/db.php
@@ -1031,4 +1031,23 @@ class Tests_DB extends WP_UnitTestCase {
 
 		$this->assertSame( 'utf8mb4_swedish_ci', $result['collate'] );
 	}
+
+	/**
+	 * @ticket 37982
+	 */
+	function test_charset_switched_to_utf8() {
+		global $wpdb;
+
+		if ( $wpdb->has_cap( 'utf8mb4' ) ) {
+			$this->markTestSkipped( 'This test requires utf8mb4 to not be supported.' );
+		}
+
+		$charset = 'utf8mb4';
+		$collate = 'utf8mb4_general_ci';
+
+		$result = $wpdb->determine_charset( $charset, $collate );
+
+		$this->assertSame( 'utf8', $result['charset'] );
+		$this->assertSame( 'utf8_general_ci', $result['collate'] );
+	}
 }