diff --git a/index.js b/index.js
index f2d163a..a4bd55c 100644
--- a/index.js
+++ b/index.js
@@ -20,6 +20,10 @@ async function subsetFont(
   text,
   { targetFormat = fontverter.detectFormat(originalFont), preserveNameIds } = {}
 ) {
+  if (typeof text !== 'string') {
+    throw new Error('The subset text must be given as a string');
+  }
+
   const [exports, heapu8] = await loadAndInitializeHarfbuzz();
 
   originalFont = await fontverter.convert(originalFont, 'truetype');
diff --git a/test/index.js b/test/index.js
index 3274a9f..f9ef8c4 100644
--- a/test/index.js
+++ b/test/index.js
@@ -25,6 +25,16 @@ describe('subset-font', function () {
       );
     });
 
+    describe('when not supplying the subset text as a string', function () {
+      it('should fail with an error', async function () {
+        await expect(
+          () => subsetFont(this.sfntFont, ['f', 'o', 'o']),
+          'to error with',
+          'The subset text must be given as a string'
+        );
+      });
+    });
+
     describe('with no targetFormat given', function () {
       it('should return the subset as truetype', async function () {
         const result = await subsetFont(this.sfntFont, 'abcd');