diff --git src/wp-includes/widgets/class-wp-widget-media-image.php src/wp-includes/widgets/class-wp-widget-media-image.php
index 780ceacad5..cc24f0e56c 100644
--- src/wp-includes/widgets/class-wp-widget-media-image.php
+++ src/wp-includes/widgets/class-wp-widget-media-image.php
@@ -177,9 +177,11 @@ class WP_Widget_Media_Image extends WP_Widget_Media {
 			$attachment = get_post( $instance['attachment_id'] );
 		}
 		if ( $attachment ) {
-			$caption = $attachment->post_excerpt;
-			if ( $instance['caption'] ) {
+			$caption = '';
+			if ( trim( $instance['caption'] ) ) {
 				$caption = $instance['caption'];
+			} elseif ( null === $instance['caption'] ) {
+				$caption = $attachment->post_excerpt;
 			}
 
 			$image_attributes = array(
diff --git tests/phpunit/tests/widgets/media-image-widget.php tests/phpunit/tests/widgets/media-image-widget.php
index 408123bef7..e68399229d 100644
--- tests/phpunit/tests/widgets/media-image-widget.php
+++ tests/phpunit/tests/widgets/media-image-widget.php
@@ -425,28 +425,38 @@ class Test_WP_Widget_Media_Image extends WP_UnitTestCase {
 		$this->assertContains( '<a href="https://example.org"', $output );
 		$this->assertContains( 'target="_blank"', $output );
 
-		// Caption settings.
+		// Populate caption in attachment.
 		wp_update_post( array(
 			'ID' => $attachment_id,
 			'post_excerpt' => 'Default caption',
 		) );
 
+		// If no caption is supplied, then the default is '', and so the caption will not be displayed.
 		ob_start();
 		$widget->render_media( array(
 			'attachment_id' => $attachment_id,
 		) );
 		$output = ob_get_clean();
+		$this->assertNotContains( 'wp-caption', $output );
+		$this->assertNotContains( '<p class="wp-caption-text">', $output );
 
+		// If the caption is explicitly null, then the caption of the underlying attachment will be displayed.
+		ob_start();
+		$widget->render_media( array(
+			'attachment_id' => $attachment_id,
+			'caption' => null,
+		) );
+		$output = ob_get_clean();
 		$this->assertContains( 'class="wp-caption alignnone"', $output );
 		$this->assertContains( '<p class="wp-caption-text">Default caption</p>', $output );
 
+		// If caption is provided, then it will be displayed.
 		ob_start();
 		$widget->render_media( array(
 			'attachment_id' => $attachment_id,
 			'caption' => 'Custom caption',
 		) );
 		$output = ob_get_clean();
-
 		$this->assertContains( 'class="wp-caption alignnone"', $output );
 		$this->assertContains( '<p class="wp-caption-text">Custom caption</p>', $output );
 	}