diff --git a/io.go b/io.go
index 2174571..d2cf764 100644
--- a/io.go
+++ b/io.go
@@ -79,6 +79,8 @@ type FileInfo struct {
 	isDir   bool
 }
 
+var _ fs.FileInfo = FileInfo{}
+
 func (info FileInfo) Name() string { return info.name }
 
 func (info FileInfo) Size() int64 { return info.size }
@@ -100,6 +102,8 @@ type DirEntry struct {
 	info  fs.FileInfo
 }
 
+var _ fs.DirEntry = DirEntry{}
+
 func (entry DirEntry) Name() string { return entry.name }
 
 func (entry DirEntry) IsDir() bool { return entry.isDir }
@@ -478,6 +482,9 @@ type MemoryFile struct {
 	modTime time.Time
 }
 
+var _ fs.File = (*MemoryFile)(nil)
+var _ goio.ReadCloser = (*MemoryFile)(nil)
+
 func (file *MemoryFile) Stat() (fs.FileInfo, error) {
 	return NewFileInfo(file.name, int64(len(file.content)), file.mode, file.modTime, false), nil
 }
@@ -503,6 +510,8 @@ type MemoryWriteCloser struct {
 	mode   fs.FileMode
 }
 
+var _ goio.WriteCloser = (*MemoryWriteCloser)(nil)
+
 func (writeCloser *MemoryWriteCloser) Write(data []byte) (int, error) {
 	writeCloser.data = append(writeCloser.data, data...)
 	return len(data), nil