diff --git a/lib/uint40_stubs.c b/lib/uint40_stubs.c
index 842a2f1..972c8f1 100644
--- a/lib/uint40_stubs.c
+++ b/lib/uint40_stubs.c
@@ -43,7 +43,7 @@ uint40_shift_right(value v1, value v2)
   CAMLreturn (copy_uint40((Uint64_val(v1) >> Int_val(v2)) & mask));
 }
 
-static const uint64_t uint40_max = 0xFFFFFFFFFF000000ULL;
+static const uint64_t uint40_max = UINT64_MAX & mask;
 static const uint64_t uint40_one = (1 << 24);
 
 CAMLprim value
diff --git a/lib/uint48_stubs.c b/lib/uint48_stubs.c
index 6a4b918..a8da153 100644
--- a/lib/uint48_stubs.c
+++ b/lib/uint48_stubs.c
@@ -43,7 +43,7 @@ uint48_shift_right(value v1, value v2)
   CAMLreturn (copy_uint48((Uint64_val(v1) >> Int_val(v2)) & mask));
 }
 
-static const uint64_t uint48_max = 0xFFFFFFFFFFFF0000ULL;
+static const uint64_t uint48_max = UINT64_MAX & mask;
 static const uint64_t uint48_one = (1 << 16);
 
 CAMLprim value
diff --git a/lib/uint56_stubs.c b/lib/uint56_stubs.c
index 3d08bf3..e3f3e35 100644
--- a/lib/uint56_stubs.c
+++ b/lib/uint56_stubs.c
@@ -43,7 +43,7 @@ uint56_shift_right(value v1, value v2)
   CAMLreturn (copy_uint56((Uint64_val(v1) >> Int_val(v2)) & mask));
 }
 
-static const uint64_t uint56_max = 0xFFFFFFFFFFFFFF00ULL;
+static const uint64_t uint56_max = UINT64_MAX & mask;
 static const uint64_t uint56_one = (1 << 8);
 
 CAMLprim value