diff --git a/index.js b/index.js
index e2f1ce0..8749a15 100644
--- a/index.js
+++ b/index.js
@@ -11,13 +11,17 @@ function md5(str) {
 }
 
 function getBodyCacheKeyJson(body) {
-  if (typeof body === 'string') {
+  if (!body) {
+    return body;
+  } if (typeof body === 'string') {
     return body;
   } if (body instanceof URLSearchParams) {
     return body.toString();
+  } if (body instanceof fs.ReadStream) {
+    return body.path;
   }
 
-  return body;
+  throw new Error('Unsupported body type');
 }
 
 function getCacheKey(requestArguments) {
diff --git a/test/tests.js b/test/tests.js
index 7e882d3..acca098 100644
--- a/test/tests.js
+++ b/test/tests.js
@@ -1,3 +1,4 @@
+const fs = require('fs');
 const assert = require('assert');
 const rimraf = require('rimraf');
 const path = require('path');
@@ -141,6 +142,27 @@ describe('Cache tests', function() {
     res = await fetch(TWO_HUNDRED_URL, post(new URLSearchParams('a=a')));
     assert.strictEqual(res.fromCache, true);
   });
+
+  it('Gives different read streams different cache keys', async function() {
+    const s1 = fs.createReadStream(__filename);
+    const s2 = fs.createReadStream(path.join(__dirname, '..', 'index.js'));
+
+    res = await fetch(TWO_HUNDRED_URL, post(s1));
+    assert.strictEqual(res.fromCache, false);
+
+    res = await fetch(TWO_HUNDRED_URL, post(s2));
+    assert.strictEqual(res.fromCache, false);
+  });
+
+  it('Gives the same read streams the same cache key', async function() {
+    const s1 = fs.createReadStream(__filename);
+
+    res = await fetch(TWO_HUNDRED_URL, post(s1));
+    assert.strictEqual(res.fromCache, false);
+
+    res = await fetch(TWO_HUNDRED_URL, post(s1));
+    assert.strictEqual(res.fromCache, true);
+  });
 }).timeout(10000);
 
 describe('Data tests', function() {