diff --git a/tests/sys_mman_test.cpp b/tests/sys_mman_test.cpp
index a71eb25..ddb6c77 100644
--- a/tests/sys_mman_test.cpp
+++ b/tests/sys_mman_test.cpp
@@ -17,6 +17,7 @@
 #include <gtest/gtest.h>
 
 #include <sys/mman.h>
+#include <sys/user.h>
 #include <sys/types.h>
 #include <unistd.h>
 
@@ -220,7 +221,7 @@
   ASSERT_EQ(MAP_FAILED, mremap(nullptr, 0, 0, 0));
 }
 
-const size_t huge = PTRDIFF_MAX + 1;
+const size_t huge = size_t(PTRDIFF_MAX) + 1;
 
 TEST(sys_mman, mmap_PTRDIFF_MAX) {
   ASSERT_EQ(MAP_FAILED, mmap(nullptr, huge, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0));