diff --git a/chrome/content/zotero/xpcom/data/item.js b/chrome/content/zotero/xpcom/data/item.js
index 70742f02cf..26ed1de4ac 100644
--- a/chrome/content/zotero/xpcom/data/item.js
+++ b/chrome/content/zotero/xpcom/data/item.js
@@ -4114,22 +4114,17 @@ Zotero.Item.prototype.toJSON = function (options = {}) {
 			let linkMode = this.attachmentLinkMode;
 			obj.linkMode = Zotero.Attachments.linkModeToName(linkMode);
 			
-			let imported = this.isImportedAttachment();
-			let skipFileProps = options.skipImportedFileProperties;
-			
-			if (!imported || !skipFileProps) {
-				obj.contentType = this.attachmentContentType;
-				obj.charset = this.attachmentCharset;
-			}
+			obj.contentType = this.attachmentContentType;
+			obj.charset = this.attachmentCharset;
 			
 			if (linkMode == Zotero.Attachments.LINK_MODE_LINKED_FILE) {
 				obj.path = this.attachmentPath;
 			}
-			else if (linkMode != Zotero.Attachments.LINK_MODE_LINKED_URL && !skipFileProps) {
+			else if (linkMode != Zotero.Attachments.LINK_MODE_LINKED_URL) {
 				obj.filename = this.attachmentFilename;
 			}
 			
-			if (imported && !skipFileProps) {
+			if (this.isImportedAttachment() && !options.skipStorageProperties) {
 				if (options.syncedStorageProperties) {
 					obj.mtime = this.attachmentSyncedModificationTime;
 					obj.md5 = this.attachmentSyncedHash;
diff --git a/chrome/content/zotero/xpcom/storage/zfs.js b/chrome/content/zotero/xpcom/storage/zfs.js
index 5d7828463b..a564530a5f 100644
--- a/chrome/content/zotero/xpcom/storage/zfs.js
+++ b/chrome/content/zotero/xpcom/storage/zfs.js
@@ -335,14 +335,6 @@ Zotero.Sync.Storage.Mode.ZFS.prototype = {
 			filename,
 			size: file.fileSize
 		};
-		var charset = item.attachmentCharset;
-		var contentType = item.attachmentContentType;
-		if (charset) {
-			json.charset = charset;
-		}
-		if (contentType) {
-			json.contentType = contentType;
-		}
 		if (zip) {
 			json.zip = true;
 		}
@@ -372,14 +364,6 @@ Zotero.Sync.Storage.Mode.ZFS.prototype = {
 			filename,
 			filesize: (yield OS.File.stat(uploadPath)).size
 		};
-		var charset = item.attachmentCharset;
-		var contentType = item.attachmentContentType;
-		if (charset) {
-			params.charset = charset;
-		}
-		if (contentType) {
-			params.contentType = contentType;
-		}
 		if (zip) {
 			params.zipMD5 = yield Zotero.Utilities.Internal.md5Async(uploadPath);
 			params.zipFilename = OS.Path.basename(uploadPath);
diff --git a/chrome/content/zotero/xpcom/sync/syncEngine.js b/chrome/content/zotero/xpcom/sync/syncEngine.js
index 88a5c335b3..cccf1e626a 100644
--- a/chrome/content/zotero/xpcom/sync/syncEngine.js
+++ b/chrome/content/zotero/xpcom/sync/syncEngine.js
@@ -878,8 +878,8 @@ Zotero.Sync.Data.Engine.prototype._uploadObjects = Zotero.Promise.coroutine(func
 					objectType,
 					o.id,
 					{
-						// Only include file properties ('contentType', etc.) for WebDAV files
-						skipImportedFileProperties:
+						// Only storage properties ('mtime', 'md5') for WebDAV files
+						skipStorageProperties:
 							objectType == 'item'
 								? Zotero.Sync.Storage.Local.getModeForLibrary(this.library.libraryID)
 									!= 'webdav'
@@ -1073,8 +1073,8 @@ Zotero.Sync.Data.Engine.prototype._getJSONForObject = function (objectType, id,
 			includeKey: true,
 			includeVersion: true, // DEBUG: remove?
 			includeDate: true,
-			// Whether to skip 'contentType', 'filename', 'mtime', and 'md5'
-			skipImportedFileProperties: options.skipImportedFileProperties,
+			// Whether to skip 'mtime' and 'md5'
+			skipStorageProperties: options.skipStorageProperties,
 			// Use last-synced mtime/md5 instead of current values from the file itself
 			syncedStorageProperties: true,
 			patchBase: cacheObj ? cacheObj.data : false
diff --git a/test/tests/itemTest.js b/test/tests/itemTest.js
index 8e5729bbd4..03cfe1f7ce 100644
--- a/test/tests/itemTest.js
+++ b/test/tests/itemTest.js
@@ -1051,6 +1051,22 @@ describe("Zotero.Item", function () {
 				assert.equal(json.md5, (yield item.attachmentHash));
 			})
 			
+			it("should omit storage values with .skipStorageProperties", function* () {
+				var file = getTestDataDirectory();
+				file.append('test.png');
+				var item = yield Zotero.Attachments.importFromFile({ file });
+				
+				item.attachmentSyncedModificationTime = new Date().getTime();
+				item.attachmentSyncedHash = 'b32e33f529942d73bea4ed112310f804';
+				yield item.saveTx({ skipAll: true });
+				
+				var json = item.toJSON({
+					skipStorageProperties: true
+				});
+				assert.isUndefined(json.mtime);
+				assert.isUndefined(json.md5);
+			});
+			
 			it("should output synced storage values with .syncedStorageProperties", function* () {
 				var item = new Zotero.Item('attachment');
 				item.attachmentLinkMode = 'imported_file';
diff --git a/test/tests/syncEngineTest.js b/test/tests/syncEngineTest.js
index 1cfb98bbb5..db6abfb91a 100644
--- a/test/tests/syncEngineTest.js
+++ b/test/tests/syncEngineTest.js
@@ -787,7 +787,7 @@ describe("Zotero.Sync.Data.Engine", function () {
 		});
 		
 		
-		it("shouldn't include file properties for attachments in ZFS libraries", function* () {
+		it("shouldn't include storage properties for attachments in ZFS libraries", function* () {
 			({ engine, client, caller } = yield setup());
 			
 			var libraryID = Zotero.Libraries.userLibraryID;
@@ -812,9 +812,9 @@ describe("Zotero.Sync.Data.Engine", function () {
 						let itemJSON = json[0];
 						assert.equal(itemJSON.key, item.key);
 						assert.equal(itemJSON.version, 0);
-						assert.notProperty(itemJSON, "contentType");
-						assert.notProperty(itemJSON, "charset");
-						assert.notProperty(itemJSON, "filename");
+						assert.property(itemJSON, "contentType");
+						assert.property(itemJSON, "charset");
+						assert.property(itemJSON, "filename");
 						assert.notProperty(itemJSON, "mtime");
 						assert.notProperty(itemJSON, "md5");
 						req.respond(
@@ -840,7 +840,7 @@ describe("Zotero.Sync.Data.Engine", function () {
 		});
 		
 		
-		it("should include file properties for attachments in WebDAV libraries", function* () {
+		it("should include storage properties for attachments in WebDAV libraries", function* () {
 			({ engine, client, caller } = yield setup());
 			
 			var libraryID = Zotero.Libraries.userLibraryID;
diff --git a/test/tests/zfsTest.js b/test/tests/zfsTest.js
index 1515be0075..14a7a5ce76 100644
--- a/test/tests/zfsTest.js
+++ b/test/tests/zfsTest.js
@@ -323,7 +323,6 @@ describe("Zotero.Sync.Storage.Mode.ZFS", function () {
 					assert.equal(params.mtime, mtime1);
 					assert.equal(params.filename, filename1);
 					assert.equal(params.filesize, size1);
-					assert.equal(params.contentType, contentType1);
 					
 					req.respond(
 						200,
@@ -375,8 +374,6 @@ describe("Zotero.Sync.Storage.Mode.ZFS", function () {
 					assert.equal(params.filename, filename2);
 					assert.equal(params.zipFilename, item2.key + ".zip");
 					assert.isTrue(parseInt(params.filesize) == params.filesize);
-					assert.equal(params.contentType, contentType2);
-					assert.equal(params.charset, charset2);
 					
 					req.respond(
 						200,