diff --git a/minix/lib/libblockdriver/const.h b/minix/lib/libblockdriver/const.h
index 1b3495bfa..4bba78001 100644
--- a/minix/lib/libblockdriver/const.h
+++ b/minix/lib/libblockdriver/const.h
@@ -2,7 +2,11 @@
 #define _BLOCKDRIVER_CONST_H
 
 /* Thread stack size. */
+#ifdef _MINIX_MAGIC
+#define STACK_SIZE	32768
+#else
 #define STACK_SIZE	8192
+#endif
 
 /* Maximum number of devices supported. */
 #define MAX_DEVICES	BLOCKDRIVER_MAX_DEVICES
diff --git a/minix/servers/vfs/worker.c b/minix/servers/vfs/worker.c
index e85d0d2be..0146be880 100644
--- a/minix/servers/vfs/worker.c
+++ b/minix/servers/vfs/worker.c
@@ -11,7 +11,9 @@ static unsigned int pending;
 static unsigned int busy;
 static int block_all;
 
-#ifdef MKCOVERAGE
+#if defined(_MINIX_MAGIC)
+# define TH_STACKSIZE (64 * 1024)
+#elif defined(MKCOVERAGE)
 # define TH_STACKSIZE (40 * 1024)
 #else
 # define TH_STACKSIZE (28 * 1024)