diff --git a/include/ndk/NdkMediaMuxer.h b/include/ndk/NdkMediaMuxer.h
index 90d946c..25987a2 100644
--- a/include/ndk/NdkMediaMuxer.h
+++ b/include/ndk/NdkMediaMuxer.h
@@ -28,6 +28,7 @@
 #ifndef _NDK_MEDIA_MUXER_H
 #define _NDK_MEDIA_MUXER_H
 
+#include <sys/cdefs.h>
 #include <sys/types.h>
 
 #include "NdkMediaCodec.h"
@@ -38,6 +39,8 @@
 extern "C" {
 #endif
 
+#if __ANDROID_API__ >= 21
+
 struct AMediaMuxer;
 typedef struct AMediaMuxer AMediaMuxer;
 
@@ -112,6 +115,8 @@
 media_status_t AMediaMuxer_writeSampleData(AMediaMuxer *muxer,
         size_t trackIdx, const uint8_t *data, const AMediaCodecBufferInfo *info);
 
+#endif /* __ANDROID_API__ >= 21 */
+
 #ifdef __cplusplus
 } // extern "C"
 #endif