diff --git a/src/js/_enqueues/wp/util.js b/src/js/_enqueues/wp/util.js
index e29fd3be462e8..61a442abc173b 100644
--- a/src/js/_enqueues/wp/util.js
+++ b/src/js/_enqueues/wp/util.js
@@ -131,6 +131,17 @@ window.wp = window.wp || {};
 								deferred.jqXHR.getResponseHeader( 'X-WP-Total' )
 							) {
 								context.totalAttachments = parseInt( deferred.jqXHR.getResponseHeader( 'X-WP-Total' ), 10 );
+
+								/*
+								 * Attachments that are still uploading can already be in the collection,
+								 * but the server does not count them yet. Add them to the total, as they
+								 * are not added to the collection again when their upload finishes.
+								 */
+								if ( _.isFunction( context.filter ) ) {
+									context.totalAttachments += context.filter( function( attachment ) {
+										return attachment.get( 'uploading' );
+									} ).length;
+								}
 							} else {
 								context.totalAttachments = 0;
 							}
diff --git a/tests/qunit/wp-includes/js/media/test-models.js b/tests/qunit/wp-includes/js/media/test-models.js
index b409d005703d2..a47f45da575c3 100644
--- a/tests/qunit/wp-includes/js/media/test-models.js
+++ b/tests/qunit/wp-includes/js/media/test-models.js
@@ -1,4 +1,4 @@
-/* globals wp */
+/* globals wp, sinon */
 /* jshint qunit: true */
 /* eslint-env qunit */
 
@@ -104,4 +104,76 @@
 			);
 		}
 	);
+
+	QUnit.module( 'wp.media.ajax total attachments', {
+		beforeEach: function () {
+			var env = this;
+
+			// Stand-in for the request; respond() answers it with 5 attachments on the server.
+			this.ajax = sinon.stub( jQuery, 'ajax' ).callsFake( function ( options ) {
+				var jqXHR = jQuery.Deferred();
+
+				jqXHR.getResponseHeader = function ( name ) {
+					return 'X-WP-Total' === name ? '5' : null;
+				};
+
+				env.respond = function () {
+					jqXHR.resolveWith( options.context, [ { success: true, data: [] } ] );
+				};
+
+				return jqXHR;
+			} );
+		},
+		afterEach: function () {
+			this.ajax.restore();
+		}
+	} );
+
+	/*
+	 * Trac #57488: when the library's query request resolves while files are
+	 * still uploading, the uploading attachments are already in the collection
+	 * but not yet counted by the server, so the total must include them.
+	 */
+	QUnit.test(
+		'the server total counts attachments that are still uploading (Trac #57488)',
+		function ( assert ) {
+			var Attachment = wp.media.model.Attachment,
+				query = new wp.media.model.Attachments();
+
+			query.add( [
+				new Attachment( { uploading: true, filename: 'one.jpg' } ),
+				new Attachment( { uploading: true, filename: 'two.jpg' } ),
+				new Attachment( { id: 3, uploading: false } )
+			] );
+
+			wp.media.ajax( {
+				context: query,
+				data: { action: 'query-attachments', query: {} }
+			} );
+			this.respond();
+
+			assert.strictEqual(
+				query.totalAttachments,
+				7,
+				'the total is the server total plus the two attachments still uploading'
+			);
+		}
+	);
+
+	QUnit.test(
+		'the server total is used as is when nothing is uploading (Trac #57488)',
+		function ( assert ) {
+			var query = new wp.media.model.Attachments();
+
+			query.add( new wp.media.model.Attachment( { id: 3 } ) );
+
+			wp.media.ajax( {
+				context: query,
+				data: { action: 'query-attachments', query: {} }
+			} );
+			this.respond();
+
+			assert.strictEqual( query.totalAttachments, 5, 'the total is the server total' );
+		}
+	);
 } )();