diff --git src/wp-includes/media.php src/wp-includes/media.php
index 8965da9ac2..614497a46b 100644
--- src/wp-includes/media.php
+++ src/wp-includes/media.php
@@ -1603,7 +1603,7 @@ function img_caption_shortcode( $attr, $content = null ) {
 
 	$style = '';
 	if ( $caption_width ) {
-		$style = 'style="max-width: ' . (int) $caption_width . 'px" ';
+		$style = 'style="width: ' . (int) $caption_width . 'px" ';
 	}
 
 	if ( $html5 ) {
diff --git tests/phpunit/tests/media.php tests/phpunit/tests/media.php
index e55a4cea97..f2961b8355 100644
--- tests/phpunit/tests/media.php
+++ tests/phpunit/tests/media.php
@@ -132,9 +132,9 @@ CAP;
 		$this->assertEquals( 1, preg_match_all( "/{$this->caption}/", $result, $_r ) );
 
 		if ( current_theme_supports( 'html5', 'caption' ) ) {
-			$this->assertEquals( 1, preg_match_all( '/max-width: 20/', $result, $_r ) );
+			$this->assertEquals( 1, preg_match_all( '/width: 20/', $result, $_r ) );
 		} else {
-			$this->assertEquals( 1, preg_match_all( '/max-width: 30/', $result, $_r ) );
+			$this->assertEquals( 1, preg_match_all( '/width: 30/', $result, $_r ) );
 		}
 	}
 
diff --git tests/phpunit/tests/shortcode.php tests/phpunit/tests/shortcode.php
index 5acd7e268f..3577fab338 100644
--- tests/phpunit/tests/shortcode.php
+++ tests/phpunit/tests/shortcode.php
@@ -535,7 +535,7 @@ EOF;
 			),
 			array(
 				'[caption caption="test" width="2"]<div>hello</div>[/caption]',
-				'<div style="max-width: 12px" class="wp-caption alignnone"><div>hello</div><p class="wp-caption-text">test</p></div>',
+				'<div style="width: 12px" class="wp-caption alignnone"><div>hello</div><p class="wp-caption-text">test</p></div>',
 			),
 			array(
 				'<div [gallery]>',