diff --git a/core.js b/core.js
index 0526f31b..10b596af 100644
--- a/core.js
+++ b/core.js
@@ -54,6 +54,11 @@ function getFileTypeFromMimeType(mimeType) {
 				ext: 'xlsx',
 				mime: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
 			};
+		case 'application/vnd.openxmlformats-officedocument.spreadsheetml.template':
+			return {
+				ext: 'xltx',
+				mime: 'application/vnd.openxmlformats-officedocument.spreadsheetml.template',
+			};
 		case 'application/vnd.openxmlformats-officedocument.wordprocessingml.document':
 			return {
 				ext: 'docx',
diff --git a/fixture/fixture.xltx b/fixture/fixture.xltx
new file mode 100644
index 00000000..988aebb2
Binary files /dev/null and b/fixture/fixture.xltx differ
diff --git a/package.json b/package.json
index 9c296e4c..2eaa2031 100644
--- a/package.json
+++ b/package.json
@@ -220,7 +220,8 @@
 		"apk",
 		"drc",
 		"lz4",
-		"potx"
+		"potx",
+		"xltx"
 	],
 	"dependencies": {
 		"@tokenizer/inflate": "^0.2.6",
diff --git a/readme.md b/readme.md
index e619d027..c25c6966 100644
--- a/readme.md
+++ b/readme.md
@@ -563,6 +563,7 @@ abortController.abort(); // Abort file-type reading from the Blob stream.
 - [`wv`](https://en.wikipedia.org/wiki/WavPack) - WavPack
 - [`xcf`](https://en.wikipedia.org/wiki/XCF_(file_format)) - eXperimental Computing Facility
 - [`xlsx`](https://en.wikipedia.org/wiki/Office_Open_XML) - Microsoft Excel document
+- [`xltx`](https://en.wikipedia.org/wiki/List_of_Microsoft_Office_filename_extensions) - Microsoft Excel template
 - [`xm`](https://wiki.openmpt.org/Manual:_Module_formats#The_FastTracker_2_format_.28.xm.29) - Audio module format: FastTracker 2
 - [`xml`](https://en.wikipedia.org/wiki/XML) - eXtensible Markup Language
 - [`xpi`](https://en.wikipedia.org/wiki/XPInstall) - XPInstall file
diff --git a/supported.js b/supported.js
index a13e6050..59c27e16 100644
--- a/supported.js
+++ b/supported.js
@@ -157,6 +157,7 @@ export const extensions = [
 	'drc',
 	'lz4',
 	'potx',
+	'xltx',
 ];
 
 export const mimeTypes = [
@@ -313,4 +314,5 @@ export const mimeTypes = [
 	'application/vnd.google.draco', // Invented by us
 	'application/x-lz4', // Invented by us
 	'application/vnd.openxmlformats-officedocument.presentationml.template',
+	'application/vnd.openxmlformats-officedocument.spreadsheetml.template',
 ];