diff --git a/test/src/unit-cbor.cpp b/test/src/unit-cbor.cpp
index 9c41dc2f..49a54999 100644
--- a/test/src/unit-cbor.cpp
+++ b/test/src/unit-cbor.cpp
@@ -28,6 +28,7 @@ SOFTWARE.
 
 #include "catch.hpp"
 
+#define private public
 #include "json.hpp"
 using nlohmann::json;
 
@@ -1262,6 +1263,12 @@ TEST_CASE("CBOR regressions")
             }
         }
     }
+
+    SECTION("improve code coverage")
+    {
+        // exotic edge case
+        CHECK_THROWS_AS(json::check_length(0xffffffffffffffff, 0xfffffffffffffff0, 0xff), std::out_of_range);
+    }
 }
 
 TEST_CASE("CBOR roundtrips", "[hide]")