diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index 73946760..d6a0e97b 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -685,7 +685,8 @@ inline bool isfinite(T value) {
 // Converts value to int and checks that it's in the range [0, upper).
 template <typename T, FMT_ENABLE_IF(std::is_integral<T>::value)>
 inline int to_nonnegative_int(T value, int upper) {
-  FMT_ASSERT(value >= 0 && value <= upper, "invalid value");
+  FMT_ASSERT(value >= 0 && to_unsigned(value) <= to_unsigned(upper),
+             "invalid value");
   (void)upper;
   return static_cast<int>(value);
 }
diff --git a/test/chrono-test.cc b/test/chrono-test.cc
index 359001a5..56507449 100644
--- a/test/chrono-test.cc
+++ b/test/chrono-test.cc
@@ -395,4 +395,8 @@ TEST(ChronoTest, SpecialDurations) {
             "03:33:20");
 }
 
+TEST(ChronoTest, UnsignedDuration) {
+  EXPECT_EQ("42s", fmt::format("{}", std::chrono::duration<unsigned>(42)));
+}
+
 #endif  // FMT_STATIC_THOUSANDS_SEPARATOR