diff --git a/compiler-rt/lib/dfsan/dfsan_custom.cpp b/compiler-rt/lib/dfsan/dfsan_custom.cpp
--- a/compiler-rt/lib/dfsan/dfsan_custom.cpp
+++ b/compiler-rt/lib/dfsan/dfsan_custom.cpp
@@ -607,8 +607,8 @@
 
 SANITIZER_INTERFACE_ATTRIBUTE
 long long unsigned int __dfsw_strtoull(const char *nptr, char **endptr,
-                                       dfsan_label nptr_label,
-                                       int base, dfsan_label endptr_label,
+                                       int base, dfsan_label nptr_label,
+                                       dfsan_label endptr_label,
                                        dfsan_label base_label,
                                        dfsan_label *ret_label) {
   char *tmp_endptr;
diff --git a/compiler-rt/test/dfsan/custom.cpp b/compiler-rt/test/dfsan/custom.cpp
--- a/compiler-rt/test/dfsan/custom.cpp
+++ b/compiler-rt/test/dfsan/custom.cpp
@@ -537,24 +537,24 @@
 }
 
 void test_strtoul() {
-  char buf[] = "0xffffffffffffaa";
+  char buf[] = "ffffffffffffaa";
   char *endptr = NULL;
   dfsan_set_label(i_label, buf + 1, 1);
   dfsan_set_label(j_label, buf + 2, 1);
   long unsigned int ret = strtol(buf, &endptr, 16);
   assert(ret == 72057594037927850);
-  assert(endptr == buf + 16);
+  assert(endptr == buf + 14);
   ASSERT_LABEL(ret, i_j_label);
 }
 
 void test_strtoull() {
-  char buf[] = "0xffffffffffffffaa";
+  char buf[] = "ffffffffffffffaa";
   char *endptr = NULL;
   dfsan_set_label(i_label, buf + 1, 1);
   dfsan_set_label(j_label, buf + 2, 1);
   long long unsigned int ret = strtoull(buf, &endptr, 16);
   assert(ret == 0xffffffffffffffaa);
-  assert(endptr == buf + 18);
+  assert(endptr == buf + 16);
   ASSERT_LABEL(ret, i_j_label);
 }