diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index 439a2a30ce..8c209ec6bf 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -2569,10 +2569,31 @@ function wp_check_filetype_and_ext( $file, $filename, $mimes = null ) {
 			 * This means that common mismatches are forgiven: application/vnd.apple.numbers is often misidentified as application/zip,
 			 * and some media files are commonly named with the wrong extension (.mov instead of .mp4)
 			 */
-
 			if ( substr( $real_mime, 0, strcspn( $real_mime, '/' ) ) !== substr( $type, 0, strcspn( $type, '/' ) ) ) {
 				$type = $ext = false;
 			}
+		} elseif ( 'text/plain' === $real_mime ) {
+			// A few common file types are occasionally detected as text/plain; allow those.
+			if ( ! in_array( $type, array(
+					'text/plain',
+					'text/csv',
+					'text/richtext',
+					'text/tsv',
+					'text/vtt',
+				) )
+			) {
+				$type = $ext = false;
+			}
+		} elseif( 'text/rtf' === $real_mime ) {
+			// Special casing for RTF files.
+			if ( ! in_array( $type, array(
+					'text/rtf',
+					'text/plain',
+					'application/rtf',
+				) )
+			) {
+				$type = $ext = false;
+			}
 		} else {
 			if ( $type !== $real_mime ) {
 				/*
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 282f832361..f9a7c51a77 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44437';
+$wp_version = '5.1-alpha-44438';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.