diff --git a/simgear/sound/openal_test1.cxx b/simgear/sound/openal_test1.cxx
index 55127b2b..0a62ef1e 100644
--- a/simgear/sound/openal_test1.cxx
+++ b/simgear/sound/openal_test1.cxx
@@ -1,4 +1,5 @@
 #include <stdio.h>
+#include <unistd.h>	// sleep()
 
 #if defined( __APPLE__ )
 # define AL_ILLEGAL_ENUM AL_INVALID_ENUM
diff --git a/simgear/sound/openal_test2.cxx b/simgear/sound/openal_test2.cxx
index 44a36e26..63353ab6 100644
--- a/simgear/sound/openal_test2.cxx
+++ b/simgear/sound/openal_test2.cxx
@@ -1,4 +1,5 @@
 #include <stdio.h>
+#include <unistd.h>	// sleep()
 
 #include "sample_openal.hxx"
 #include "soundmgr_openal.hxx"