diff --git a/examples/spectrogram/fft.h b/examples/spectrogram/fft.h
index b744d54..31b6da7 100644
--- a/examples/spectrogram/fft.h
+++ b/examples/spectrogram/fft.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <cmath>
+#include <stdlib.h>
 
 // FFT routines taken from https://stackoverflow.com/a/37729648/4039976