diff --git a/libs/pbd/pbd/pthread_utils.h b/libs/pbd/pbd/pthread_utils.h
index c2bd49ccb6..741493a41f 100644
--- a/libs/pbd/pbd/pthread_utils.h
+++ b/libs/pbd/pbd/pthread_utils.h
@@ -48,7 +48,12 @@
 #include "pbd/libpbd_visibility.h"
 #include "pbd/signals.h"
 
-#define PBD_RT_STACKSIZE_PROC 0x20000 // 128kB
+#ifdef __APPLE__
+# define PBD_RT_STACKSIZE_PROC 0x80000 // 512kB
+#else
+# define PBD_RT_STACKSIZE_PROC 0x20000 // 128kB
+#endif
+
 #define PBD_RT_STACKSIZE_HELP 0x08000 // 32kB
 
 /* these are relative to sched_get_priority_max()