diff --git a/src/beep.h b/src/beep.h
index e3ebf83..9416409 100644
--- a/src/beep.h
+++ b/src/beep.h
@@ -20,6 +20,12 @@ typedef struct
     uint32_t freq;
 } paTestData;
 
+static int patestCallback( const void *inputBuffer, void *outputBuffer,
+                           unsigned long framesPerBuffer,
+                           const PaStreamCallbackTimeInfo* timeInfo,
+                           PaStreamCallbackFlags statusFlags,
+                           void *userData );
+
 void buzzer_set_freq(int frequency);
 void buzzer_beep(int frequency, int msecs);
 int buzzer_start(void);