diff --git a/src/internal/pthread_impl.h b/src/internal/pthread_impl.h
index 26e6e1df..e73a251f 100644
--- a/src/internal/pthread_impl.h
+++ b/src/internal/pthread_impl.h
@@ -182,12 +182,15 @@ hidden void __acquire_ptc(void);
 hidden void __release_ptc(void);
 hidden void __inhibit_ptc(void);
 
-extern hidden size_t __default_stacksize;
-extern hidden size_t __default_guardsize;
+extern hidden unsigned __default_stacksize;
+extern hidden unsigned __default_guardsize;
 
 #define DEFAULT_STACK_SIZE 81920
 #define DEFAULT_GUARD_SIZE 4096
 
+#define DEFAULT_STACK_MAX (8<<20)
+#define DEFAULT_GUARD_MAX (1<<20)
+
 #define __ATTRP_C11_THREAD ((void*)(uintptr_t)-1)
 
 #endif
diff --git a/src/thread/default_attr.c b/src/thread/default_attr.c
index 46fe98ee..dce96409 100644
--- a/src/thread/default_attr.c
+++ b/src/thread/default_attr.c
@@ -1,4 +1,4 @@
 #include "pthread_impl.h"
 
-size_t __default_stacksize = DEFAULT_STACK_SIZE;
-size_t __default_guardsize = DEFAULT_GUARD_SIZE;
+unsigned __default_stacksize = DEFAULT_STACK_SIZE;
+unsigned __default_guardsize = DEFAULT_GUARD_SIZE;
diff --git a/src/thread/pthread_setattr_default_np.c b/src/thread/pthread_setattr_default_np.c
index 256f0685..58486220 100644
--- a/src/thread/pthread_setattr_default_np.c
+++ b/src/thread/pthread_setattr_default_np.c
@@ -2,6 +2,9 @@
 #include "pthread_impl.h"
 #include <string.h>
 
+#define MIN(a,b) ((a)<(b) ? (a) : (b))
+#define MAX(a,b) ((a)>(b) ? (a) : (b))
+
 int pthread_setattr_default_np(const pthread_attr_t *attrp)
 {
 	/* Reject anything in the attr object other than stack/guard size. */
@@ -11,11 +14,12 @@ int pthread_setattr_default_np(const pthread_attr_t *attrp)
 	if (memcmp(&tmp, &zero, sizeof tmp))
 		return EINVAL;
 
+	unsigned stack = MIN(attrp->_a_stacksize, DEFAULT_STACK_MAX);
+	unsigned guard = MIN(attrp->_a_guardsize, DEFAULT_GUARD_MAX);
+
 	__inhibit_ptc();
-	if (attrp->_a_stacksize >= __default_stacksize)
-		__default_stacksize = attrp->_a_stacksize;
-	if (attrp->_a_guardsize >= __default_guardsize)
-		__default_guardsize = attrp->_a_guardsize;
+	__default_stacksize = MAX(__default_stacksize, stack);
+	__default_guardsize = MAX(__default_guardsize, guard);
 	__release_ptc();
 
 	return 0;