diff --git a/include/CLI/StringTools.hpp b/include/CLI/StringTools.hpp
index 44f4a0e24..14fd1aee1 100644
--- a/include/CLI/StringTools.hpp
+++ b/include/CLI/StringTools.hpp
@@ -141,15 +141,15 @@ CLI11_INLINE std::ostream &format_aliases(std::ostream &out, const std::vector<s
 /// Verify the first character of an option
 /// - is a trigger character, ! has special meaning and new lines would just be annoying to deal with
 template <typename T> bool valid_first_char(T c) {
-    return ((c != '-') && (c != '!') && (c != ' ') && (c != '\n') && (c != '\0'));
+    return ((c != '-') && (static_cast<unsigned char>(c) > 33)); // space and '!' not allowed
 }
 
 /// Verify following characters of an option
 template <typename T> bool valid_later_char(T c) {
     // = and : are value separators, { has special meaning for option defaults,
-    // and \n and '\0' would just be annoying to deal with in many places allowing space here has too much potential for
+    // and control codes other than tab would just be annoying to deal with in many places allowing space here has too much potential for
     // inadvertent entry errors and bugs
-    return ((c != '=') && (c != ':') && (c != '{') && (c != ' ') && (c != '\n') && (c != '\0'));
+    return ((c != '=') && (c != ':') && (c != '{') && ((static_cast<unsigned char>(c) > 32)||c=='\t'));
 }
 
 /// Verify an option/subcommand name
diff --git a/include/CLI/impl/App_inl.hpp b/include/CLI/impl/App_inl.hpp
index 4a582dd56..7251a5e49 100644
--- a/include/CLI/impl/App_inl.hpp
+++ b/include/CLI/impl/App_inl.hpp
@@ -371,13 +371,13 @@ CLI11_INLINE bool App::remove_option(Option *opt) {
 CLI11_INLINE App *App::add_subcommand(std::string subcommand_name, std::string subcommand_description) {
     if(!subcommand_name.empty() && !detail::valid_name_string(subcommand_name)) {
         if(!detail::valid_first_char(subcommand_name[0])) {
-            throw IncorrectConstruction("Subcommand name starts with invalid character, '!' and '-' are not allowed");
+            throw IncorrectConstruction("Subcommand name starts with invalid character, '!' and '-' and control characters");
         }
         for(auto c : subcommand_name) {
             if(!detail::valid_later_char(c)) {
                 throw IncorrectConstruction(std::string("Subcommand name contains invalid character ('") + c +
                                             "'), all characters are allowed except"
-                                            "'=',':','{','}', and ' '");
+                                            "'=',':','{','}', ' ', and control characters");
             }
         }
     }
diff --git a/tests/FuzzFailTest.cpp b/tests/FuzzFailTest.cpp
index a4bf57ed9..1d2e15070 100644
--- a/tests/FuzzFailTest.cpp
+++ b/tests/FuzzFailTest.cpp
@@ -63,7 +63,7 @@ TEST_CASE("app_file_gen_fail") {
     CLI::FuzzApp fuzzdata;
     auto app = fuzzdata.generateApp();
 
-    int index = GENERATE(range(1, 9));
+    int index = GENERATE(range(1, 10));
     std::string optionString, flagString;
     auto parseData = loadFailureFile("fuzz_app_file_fail", index);
     if(parseData.size() > 25) {
diff --git a/tests/fuzzFail/fuzz_app_file_fail9 b/tests/fuzzFail/fuzz_app_file_fail9
new file mode 100644
index 000000000..1c8303c41
--- /dev/null
+++ b/tests/fuzzFail/fuzz_app_file_fail9
@@ -0,0 +1 @@
+=oÿÿÿÿÿÿÿÿÿÿp--2vÿÿt'Í-è-
\ No newline at end of file