diff --git a/libs/pbd/pbd/control_math.h b/libs/pbd/pbd/control_math.h
index 8ead1c918a..9a59a3c9e5 100644
--- a/libs/pbd/pbd/control_math.h
+++ b/libs/pbd/pbd/control_math.h
@@ -22,6 +22,7 @@
 
 #include <assert.h>
 #include <math.h>
+#include <stdint.h>
 
 /* map gain-coeff [0..2] to position [0..1] */
 static inline double