diff --git a/test/scan-test.cc b/test/scan-test.cc
index 93084c1d..f0ede192 100644
--- a/test/scan-test.cc
+++ b/test/scan-test.cc
@@ -63,6 +63,9 @@ TEST(scan_test, read_hex) {
   unsigned n = 0;
   fmt::scan("2a", "{:x}", n);
   EXPECT_EQ(n, 42);
+  auto num_digits = std::numeric_limits<unsigned>::digits / 4;
+  EXPECT_THROW_MSG(fmt::scan(fmt::format("1{:0{}}", 0, num_digits), "{:x}", n),
+                   fmt::format_error, "number is too big");
 }
 
 TEST(scan_test, read_string) {
diff --git a/test/scan.h b/test/scan.h
index 0ced8f39..a68c77c3 100644
--- a/test/scan.h
+++ b/test/scan.h
@@ -499,18 +499,19 @@ auto read_hex(scan_iterator it, T& value)
     if (digit < 0) break;
   } while (it != scan_sentinel());
 
-  // TODO: Check overflow.
-  (void)num_digits;
-  value = n;
+  // Check overflow.
+  if (num_digits <= (std::numeric_limits<T>::digits >> 2))
+    value = n;
+  else
+    throw_format_error("number is too big");
   return it;
 }
 
 template <typename T, FMT_ENABLE_IF(std::is_unsigned<T>::value)>
 auto read(scan_iterator it, T& value, const format_specs<>& specs)
     -> scan_iterator {
-  if (specs.type == presentation_type::hex_lower) {
+  if (specs.type == presentation_type::hex_lower)
     return read_hex(it, value);
-  }
   return read(it, value);
 }