diff --git a/include/ndk/NdkMediaCodec.h b/include/ndk/NdkMediaCodec.h
index fcb3a99..ad17321 100644
--- a/include/ndk/NdkMediaCodec.h
+++ b/include/ndk/NdkMediaCodec.h
@@ -27,6 +27,8 @@
 #ifndef _NDK_MEDIA_CODEC_H
 #define _NDK_MEDIA_CODEC_H
 
+#include <sys/cdefs.h>
+
 #include <android/native_window.h>
 
 #include "NdkMediaCrypto.h"
@@ -37,6 +39,7 @@
 extern "C" {
 #endif
 
+#if __ANDROID_API__ >= 21
 
 struct AMediaCodec;
 typedef struct AMediaCodec AMediaCodec;
@@ -254,6 +257,8 @@
  */
 media_status_t AMediaCodecCryptoInfo_getEncryptedBytes(AMediaCodecCryptoInfo*, size_t *dst);
 
+#endif /* __ANDROID_API__ >= 21 */
+
 #ifdef __cplusplus
 } // extern "C"
 #endif