--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -683,9 +692,13 @@
 			prot) != 0)
 	    goto mprot_error;
 #elif _STACK_GROWS_UP
-	  if (mprotect ((char *) pd - pd->guardsize,
-			pd->guardsize - guardsize, prot) != 0)
-	    goto mprot_error;
+	  char *new_guard = (char *) (((uintptr_t) pd - guardsize) & ~pagesize_m1);
+	  char *old_guard = (char *) (((uintptr_t) pd - pd->guardsize) & ~pagesize_m1);
+	  /* The guard size difference might be > 0, but once rounded
+	     to the nearest page the size difference might be zero.  */
+	  if (old_guard - new_guard > 0)
+	    if (mprotect (old_guard, new_guard - old_guard, prot) != 0)
+	      goto mprot_error;
 #endif
 
 	  pd->guardsize = guardsize;