diff --git src/wp-includes/functions.php src/wp-includes/functions.php
index d4af13f..03508e8 100644
--- src/wp-includes/functions.php
+++ src/wp-includes/functions.php
@@ -2491,7 +2491,7 @@ function wp_get_mime_types() {
 	'3gp|3gpp' => 'video/3gpp', // Can also be audio
 	'3g2|3gp2' => 'video/3gpp2', // Can also be audio
 	// Text formats.
-	'txt|asc|c|cc|h|srt' => 'text/plain',
+	'txt|asc|c|cc|h|srt|csv' => 'text/plain',
 	'csv' => 'text/csv',
 	'tsv' => 'text/tab-separated-values',
 	'ics' => 'text/calendar',
diff --git tests/phpunit/data/uploads/sample.csv tests/phpunit/data/uploads/sample.csv
new file mode 100644
index 0000000..8e038b3
--- /dev/null
+++ tests/phpunit/data/uploads/sample.csv
@@ -0,0 +1,4 @@
+"country","country group","name (en)","name (fr)","name (de)","latitude","longitude"
+"at","eu","Austria","Autriche","Österreich","47.6965545","13.34598005"
+"be","eu","Belgium","Belgique","Belgien","50.501045","4.47667405"
+"bg","eu","Bulgaria","Bulgarie","Bulgarien","42.72567375","25.4823218"
diff --git tests/phpunit/tests/functions.php tests/phpunit/tests/functions.php
index 9a1aef0..d2b884c 100644
--- tests/phpunit/tests/functions.php
+++ tests/phpunit/tests/functions.php
@@ -1185,6 +1185,16 @@ class Tests_Functions extends WP_UnitTestCase {
 						'proper_filename' => false,
 					),
 				),
+				// CSV file.
+				array(
+					DIR_TESTDATA . '/uploads/sample.csv',
+					'sample.csv',
+					array(
+						'ext'             => 'csv',
+						'type'            => 'text/plain',
+						'proper_filename' => false,
+					),
+				),
 			) );
 		}