diff --git a/configure.ac b/configure.ac
index a1580b650..20285b17c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2506,11 +2506,12 @@ case "$ac_cv_prog_gcc" in yes)
             CFLAGS_FOR_GOTOS="$CFLAGS_FOR_GOTOS -fomit-frame-pointer"
             ;;
         i*86-*|x86_64*)
-            # On x86-64 with GCC 4.8, gcc labels do not work correctly with
-            # -ftree-dominator-opts -- we disable it for x86 in this case too.
+            # On x86-64 with GCC 4.8 and 4.9 gcc labels do not work correctly
+            # with -ftree-dominator-opts -- we disable it for x86 in this case
+            # too.
             #
             case "$C_COMPILER_TYPE" in
-                gcc_4_8_*)
+                gcc_4_8_*|gcc_4_9_*)
                   CFLAGS_FOR_GOTOS="$CFLAGS_FOR_GOTOS -fno-tree-dominator-opts"
                 ;;
             esac
diff --git a/runtime/mercury_stack_trace.c b/runtime/mercury_stack_trace.c
index 708adee8a..9cc6d252b 100644
--- a/runtime/mercury_stack_trace.c
+++ b/runtime/mercury_stack_trace.c
@@ -1265,7 +1265,8 @@ MR_dump_nondet_stack_from_layout(FILE *fp,
         } else {
             frame_size = apparent_frame_size;
             MR_print_nondetstackptr(fp, base_maxfr);
-            fprintf(fp, ": ordinary, %d words", frame_size);
+            fprintf(fp, ": ordinary, %" MR_INTEGER_LENGTH_MODIFIER "d words",
+                frame_size);
             if (print_vars && MR_find_matching_branch(base_maxfr, &branch)) {
                 fprintf(fp, ", ");
                 label_layout = MR_nondet_branch_infos[branch].branch_layout;