diff --git a/src/audio/SDL_audio_c.h b/src/audio/SDL_audio_c.h
index 5d1d554ee..767fb8d4f 100644
--- a/src/audio/SDL_audio_c.h
+++ b/src/audio/SDL_audio_c.h
@@ -18,6 +18,10 @@
      misrepresented as being the original software.
   3. This notice may not be removed or altered from any source distribution.
 */
+
+#ifndef SDL_audio_c_h_
+#define SDL_audio_c_h_
+
 #include "../SDL_internal.h"
 
 #ifndef DEBUG_CONVERT
@@ -94,4 +98,6 @@ int SDL_AudioStreamAvailable(SDL_AudioStream *stream);
 /* dispose of a stream */
 void SDL_FreeAudioStream(SDL_AudioStream *stream);
 
+#endif
+
 /* vi: set ts=4 sw=4 expandtab: */
diff --git a/src/audio/SDL_sysaudio.h b/src/audio/SDL_sysaudio.h
index bad295088..e62aecf68 100644
--- a/src/audio/SDL_sysaudio.h
+++ b/src/audio/SDL_sysaudio.h
@@ -26,6 +26,7 @@
 #include "SDL_mutex.h"
 #include "SDL_thread.h"
 #include "../SDL_dataqueue.h"
+#include "./SDL_audio_c.h"
 
 /* !!! FIXME: These are wordy and unlocalized... */
 #define DEFAULT_OUTPUT_DEVNAME "System audio output device"
@@ -35,8 +36,6 @@
 typedef struct SDL_AudioDevice SDL_AudioDevice;
 #define _THIS   SDL_AudioDevice *_this
 
-typedef struct SDL_AudioStream SDL_AudioStream;
-
 /* Audio targets should call this as devices are added to the system (such as
    a USB headset being plugged in), and should also be called for
    for every device found during DetectDevices(). */