diff --git a/miniaudio.h b/miniaudio.h
index 6aa76fe4..ce2a6db6 100644
--- a/miniaudio.h
+++ b/miniaudio.h
@@ -6310,6 +6310,13 @@ static void ma_device__send_frames_to_client(ma_device* pDevice, ma_uint32 frame
     }
 }
 
+
+/* We only want to expose ma_device__handle_duplex_callback_capture() and ma_device__handle_duplex_callback_playback() if we have an asynchronous backend enabled. */
+#if defined(MA_HAS_JACK)      || \
+    defined(MA_HAS_COREAUDIO) || \
+    defined(MA_HAS_AAUDIO)    || \
+    defined(MA_HAS_OPENSL)    || \
+    defined(MA_HAS_WEBAUDIO)
 static ma_result ma_device__handle_duplex_callback_capture(ma_device* pDevice, ma_uint32 frameCountInDeviceFormat, const void* pFramesInDeviceFormat, ma_pcm_rb* pRB)
 {
     ma_result result;
@@ -6444,6 +6451,7 @@ static ma_result ma_device__handle_duplex_callback_playback(ma_device* pDevice,
 
     return MA_SUCCESS;
 }
+#endif  /* Asynchronous backends. */
 
 /* A helper for changing the state of the device. */
 static MA_INLINE void ma_device__set_state(ma_device* pDevice, ma_uint32 newState)