diff --git a/include/beman/inplace_vector/inplace_vector.hpp b/include/beman/inplace_vector/inplace_vector.hpp
index 4395f45..d499fc2 100644
--- a/include/beman/inplace_vector/inplace_vector.hpp
+++ b/include/beman/inplace_vector/inplace_vector.hpp
@@ -47,10 +47,10 @@ inline constexpr from_range_t from_range;
 // Smallest unsigned integer that can represent values in [0, N].
 template <size_t N>
 using smallest_size_t
-= std::conditional_t<(N < std::numeric_limits<uint8_t>::max()),  uint8_t,
-    std::conditional_t<(N < std::numeric_limits<uint16_t>::max()), uint16_t,
-    std::conditional_t<(N < std::numeric_limits<uint32_t>::max()), uint32_t,
-    std::conditional_t<(N < std::numeric_limits<uint64_t>::max()), uint64_t,
+= std::conditional_t<(N <= std::numeric_limits<uint8_t>::max()),  uint8_t,
+    std::conditional_t<(N <= std::numeric_limits<uint16_t>::max()), uint16_t,
+    std::conditional_t<(N <= std::numeric_limits<uint32_t>::max()), uint32_t,
+    std::conditional_t<(N <= std::numeric_limits<uint64_t>::max()), uint64_t,
                    size_t>>>>;
 // clang-format on
 
diff --git a/tests/beman/inplace_vector/size_n_data.test.cpp b/tests/beman/inplace_vector/size_n_data.test.cpp
index a3595be..b3f66ae 100644
--- a/tests/beman/inplace_vector/size_n_data.test.cpp
+++ b/tests/beman/inplace_vector/size_n_data.test.cpp
@@ -1,9 +1,25 @@
 #include <gtest/gtest.h>
 #include <numeric>
 
+#include <cstdint>
+
 #include "gtest_setup.hpp"
 
 namespace {
+// details::smallest_size_t — smallest unsigned integer holding values in [0, N]
+using beman::inplace_vector::details::smallest_size_t;
+static_assert(std::is_same_v<smallest_size_t<0>, uint8_t>);
+static_assert(std::is_same_v<smallest_size_t<255>, uint8_t>);
+static_assert(std::is_same_v<smallest_size_t<256>, uint16_t>);
+static_assert(std::is_same_v<smallest_size_t<65535>, uint16_t>);
+static_assert(std::is_same_v<smallest_size_t<65536>, uint32_t>);
+static_assert(std::is_same_v<
+              smallest_size_t<std::numeric_limits<uint32_t>::max()>, uint32_t>);
+static_assert(
+    std::is_same_v<
+        smallest_size_t<std::size_t{1} + std::numeric_limits<uint32_t>::max()>,
+        uint64_t>);
+
 // 23.3.14.3 Size and capacity [inplace.vector.capacity]
 
 template <typename Param> class SizeNCapacity : public IVBasicTest<Param> {};