diff --git a/README.md b/README.md
index 330f786..b7aa998 100644
--- a/README.md
+++ b/README.md
@@ -86,7 +86,7 @@ Returns `true` if a file or folder at the specified path exists.
 ### `isDirectorySync(directoryPath)`
 Returns `true` if the given path exists and is a directory.
 
-### `isDirectory(directoryPath)`
+### `isDirectory(directoryPath, callback)`
 Asynchronously checks that the given path exists and is a directory.
 
 ### `isFileSync(filePath)`