diff --git a/extern/json b/extern/json
index f1768a54..db53bdac 160000
--- a/extern/json
+++ b/extern/json
@@ -1 +1 @@
-Subproject commit f1768a540a7b7c5cc30cdcd6be9e9ef91083719b
+Subproject commit db53bdac1926d1baebcb459b685dcd2e4608c355
diff --git a/tests/CreationTest.cpp b/tests/CreationTest.cpp
index 508c6a1d..d8fa4dd7 100644
--- a/tests/CreationTest.cpp
+++ b/tests/CreationTest.cpp
@@ -48,6 +48,20 @@ TEST_F(TApp, AddingExistingWithCaseAfter2) {
     EXPECT_THROW(cat->ignore_case(), CLI::OptionAlreadyAdded);
 }
 
+TEST_F(TApp, AddingExistingWithUnderscoreAfter) {
+    auto count = app.add_flag("--underscore");
+    app.add_flag("--under_score");
+
+    EXPECT_THROW(count->ignore_underscore(), CLI::OptionAlreadyAdded);
+}
+
+TEST_F(TApp, AddingExistingWithUnderscoreAfter2) {
+    auto count = app.add_flag("--under_score");
+    app.add_flag("--underscore");
+
+    EXPECT_THROW(count->ignore_underscore(), CLI::OptionAlreadyAdded);
+}
+
 TEST_F(TApp, AddingMultipleInfPositionals) {
     std::vector<std::string> one, two;
     app.add_option("one", one);