diff --git a/src/os.cpp b/src/os.cpp
index 5d43e73d8aeedaa651d7080931e8c7104f4636ae..9d16d763ec8dc7ecd722270c08e8450af836007e 100644
--- a/src/os.cpp
+++ b/src/os.cpp
@@ -1976,7 +1976,7 @@ Error os_file_read(OsFile file, void *ptr, size_t *len) {
                 case EFAULT:
                     zig_unreachable();
                 case EISDIR:
-                    zig_unreachable();
+                    return ErrorIsDir;
                 default:
                     return ErrorFileSystem;
             }