diff --git a/src/CacheFS.js b/src/CacheFS.js
index bb8c6b2..0345b98 100755
--- a/src/CacheFS.js
+++ b/src/CacheFS.js
@@ -1,5 +1,5 @@
 const path = require("./path.js");
-const { ENOENT, EEXIST, ENOTEMPTY } = require("./errors.js");
+const { EEXIST, ENOENT, ENOTDIR, ENOTEMPTY } = require("./errors.js");
 
 const STAT = 0;
 
@@ -149,8 +149,10 @@ module.exports = class CacheFS {
     dir.set(basename, entry);
   }
   rmdir(filepath) {
+    let dir = this._lookup(filepath);
+    if (dir.get(STAT).type !== 'dir') throw new ENOTDIR();
     // check it's empty (size should be 1 for just StatSym)
-    if (this._lookup(filepath).size > 1) throw new ENOTEMPTY();
+    if (dir.size > 1) throw new ENOTEMPTY();
     // remove from parent
     let parent = this._lookup(path.dirname(filepath));
     let basename = path.basename(filepath);
@@ -158,6 +160,7 @@ module.exports = class CacheFS {
   }
   readdir(filepath) {
     let dir = this._lookup(filepath);
+    if (dir.get(STAT).type !== 'dir') throw new ENOTDIR();
     return [...dir.keys()].filter(key => typeof key === "string");
   }
   writeFile(filepath, data, { mode }) {
diff --git a/src/__tests__/fs.promises.spec.js b/src/__tests__/fs.promises.spec.js
index d194377..40a24c0 100755
--- a/src/__tests__/fs.promises.spec.js
+++ b/src/__tests__/fs.promises.spec.js
@@ -152,6 +152,17 @@ describe("fs.promises module", () => {
         });
       });
     });
+    it("read a file throws", done => {
+      fs.mkdir("/readdir2").finally(() => {
+        fs.writeFile("/readdir2/not-a-dir", "").then(() => {
+          fs.readdir("/readdir2/not-a-dir").catch(err => {
+            expect(err).not.toBe(null);
+            expect(err.code).toBe('ENOTDIR');
+            done();
+          });
+        })
+      })
+    });
   });
 
   describe("rmdir", () => {
@@ -199,6 +210,17 @@ describe("fs.promises module", () => {
         });
       });
     });
+    it("delete a file throws", done => {
+      fs.mkdir("/rmdir").finally(() => {
+        fs.writeFile("/rmdir/not-a-dir", "").then(() => {
+          fs.rmdir("/rmdir/not-a-dir").catch(err => {
+            expect(err).not.toBe(null);
+            expect(err.code).toBe('ENOTDIR');
+            done();
+          });
+        });
+      });
+    });
   });
 
   describe("unlink", () => {
diff --git a/src/errors.js b/src/errors.js
index fe4408b..8ea3626 100755
--- a/src/errors.js
+++ b/src/errors.js
@@ -14,6 +14,7 @@ function Err(name) {
 
 const EEXIST = Err("EEXIST");
 const ENOENT = Err("ENOENT");
+const ENOTDIR = Err("ENOTDIR");
 const ENOTEMPTY = Err("ENOTEMPTY");
 
-module.exports = { EEXIST, ENOENT, ENOTEMPTY };
+module.exports = { EEXIST, ENOENT, ENOTDIR, ENOTEMPTY };