diff --git a/include/CLI/TypeTools.hpp b/include/CLI/TypeTools.hpp
index 17997446d..0d2daef80 100644
--- a/include/CLI/TypeTools.hpp
+++ b/include/CLI/TypeTools.hpp
@@ -861,7 +861,7 @@ bool integral_conversion(const std::string &input, T &output) noexcept {
     if(input.empty() || input.front() == '-') {
         return false;
     }
-    char *val = nullptr;
+    char *val{nullptr};
     errno = 0;
     std::uint64_t output_ll = std::strtoull(input.c_str(), &val, 0);
     if(errno == ERANGE) {
@@ -904,8 +904,8 @@ bool integral_conversion(const std::string &input, T &output) noexcept {
     return false;
 }
 
-/// Convert a flag into an integer value  typically binary flags
-inline std::int64_t to_flag_value(std::string val) {
+/// Convert a flag into an integer value  typically binary flags sets errno to nonzero if conversion failed
+inline std::int64_t to_flag_value(std::string val) noexcept {
     static const std::string trueString("true");
     static const std::string falseString("false");
     if(val == trueString) {
@@ -933,7 +933,8 @@ inline std::int64_t to_flag_value(std::string val) {
             ret = 1;
             break;
         default:
-            throw std::invalid_argument("unrecognized character");
+            errno = EINVAL;
+            return -1;
         }
         return ret;
     }
@@ -942,7 +943,11 @@ inline std::int64_t to_flag_value(std::string val) {
     } else if(val == falseString || val == "off" || val == "no" || val == "disable") {
         ret = -1;
     } else {
-        ret = std::stoll(val);
+        char *loc_ptr{nullptr};
+        ret = std::strtoll(val.c_str(), &loc_ptr, 0);
+        if(loc_ptr != (val.c_str() + val.size()) && errno == 0) {
+            errno = EINVAL;
+        }
     }
     return ret;
 }
@@ -971,18 +976,16 @@ bool lexical_cast(const std::string &input, T &output) {
 template <typename T,
           enable_if_t<classify_object<T>::value == object_category::boolean_value, detail::enabler> = detail::dummy>
 bool lexical_cast(const std::string &input, T &output) {
-    try {
-        auto out = to_flag_value(input);
+    errno = 0;
+    auto out = to_flag_value(input);
+    if(errno == 0) {
         output = (out > 0);
-        return true;
-    } catch(const std::invalid_argument &) {
-        return false;
-    } catch(const std::out_of_range &) {
-        // if the number is out of the range of a 64 bit value then it is still a number and for this purpose is still
-        // valid all we care about the sign
+    } else if(errno == ERANGE) {
         output = (input[0] != '-');
-        return true;
+    } else {
+        return false;
     }
+    return true;
 }
 
 /// Floats
@@ -1638,12 +1641,13 @@ inline std::string sum_string_vector(const std::vector<std::string> &values) {
         double tv{0.0};
         auto comp = lexical_cast(arg, tv);
         if(!comp) {
-            try {
-                tv = static_cast<double>(detail::to_flag_value(arg));
-            } catch(const std::exception &) {
-                fail = true;
+            errno = 0;
+            auto fv = detail::to_flag_value(arg);
+            fail = (errno != 0);
+            if(fail) {
                 break;
             }
+            tv = static_cast<double>(fv);
         }
         val += tv;
     }
diff --git a/include/CLI/impl/App_inl.hpp b/include/CLI/impl/App_inl.hpp
index fd8c375a5..5e703eddf 100644
--- a/include/CLI/impl/App_inl.hpp
+++ b/include/CLI/impl/App_inl.hpp
@@ -1431,18 +1431,15 @@ CLI11_INLINE bool App::_parse_single_config(const ConfigItem &item, std::size_t
                 auto res = config_formatter_->to_flag(item);
                 bool converted{false};
                 if(op->get_disable_flag_override()) {
-
-                    try {
-                        auto val = detail::to_flag_value(res);
-                        if(val == 1) {
-                            res = op->get_flag_value(item.name, "{}");
-                            converted = true;
-                        }
-                    } catch(...) {
+                    auto val = detail::to_flag_value(res);
+                    if(val == 1) {
+                        res = op->get_flag_value(item.name, "{}");
+                        converted = true;
                     }
                 }
 
                 if(!converted) {
+                    errno = 0;
                     res = op->get_flag_value(item.name, res);
                 }
 
diff --git a/include/CLI/impl/Option_inl.hpp b/include/CLI/impl/Option_inl.hpp
index a24df9ab2..250b626b6 100644
--- a/include/CLI/impl/Option_inl.hpp
+++ b/include/CLI/impl/Option_inl.hpp
@@ -389,15 +389,15 @@ CLI11_NODISCARD CLI11_INLINE std::string Option::get_flag_value(const std::strin
         return input_value;
     }
     if(default_flag_values_[static_cast<std::size_t>(ind)].second == falseString) {
-        try {
-            auto val = detail::to_flag_value(input_value);
-            return (val == 1) ? falseString : (val == (-1) ? trueString : std::to_string(-val));
-        } catch(const std::invalid_argument &) {
+        errno = 0;
+        auto val = detail::to_flag_value(input_value);
+        if(errno != 0) {
+            errno = 0;
             return input_value;
         }
-    } else {
-        return input_value;
+        return (val == 1) ? falseString : (val == (-1) ? trueString : std::to_string(-val));
     }
+    return input_value;
 }
 
 CLI11_INLINE Option *Option::add_result(std::string s) {
diff --git a/tests/FuzzFailTest.cpp b/tests/FuzzFailTest.cpp
index 8b2e30383..97965888c 100644
--- a/tests/FuzzFailTest.cpp
+++ b/tests/FuzzFailTest.cpp
@@ -45,3 +45,16 @@ TEST_CASE("app_fail") {
     } catch(const CLI::ConstructionError & /*e*/) {
     }
 }
+
+TEST_CASE("file_fail") {
+    CLI::FuzzApp fuzzdata;
+    auto app = fuzzdata.generateApp();
+
+    int index = GENERATE(range(1, 2));
+    auto parseData = loadFailureFile("fuzz_file_fail", index);
+    std::stringstream out(parseData);
+    try {
+        app->parse_from_stream(out);
+    } catch(const CLI::ParseError & /*e*/) {
+    }
+}
diff --git a/tests/HelpersTest.cpp b/tests/HelpersTest.cpp
index d92d3fcef..529cfa69f 100644
--- a/tests/HelpersTest.cpp
+++ b/tests/HelpersTest.cpp
@@ -201,15 +201,26 @@ TEST_CASE("StringTools: Modify3", "[helpers]") {
 }
 
 TEST_CASE("StringTools: flagValues", "[helpers]") {
+    errno = 0;
     CHECK(-1 == CLI::detail::to_flag_value("0"));
+    CHECK(errno == 0);
     CHECK(1 == CLI::detail::to_flag_value("t"));
     CHECK(1 == CLI::detail::to_flag_value("1"));
     CHECK(6 == CLI::detail::to_flag_value("6"));
     CHECK(-6 == CLI::detail::to_flag_value("-6"));
     CHECK(-1 == CLI::detail::to_flag_value("false"));
     CHECK(1 == CLI::detail::to_flag_value("YES"));
-    CHECK_THROWS_AS(CLI::detail::to_flag_value("frog"), std::invalid_argument);
-    CHECK_THROWS_AS(CLI::detail::to_flag_value("q"), std::invalid_argument);
+    errno = 0;
+    CLI::detail::to_flag_value("frog");
+    CHECK(errno == EINVAL);
+    errno = 0;
+    CLI::detail::to_flag_value("q");
+    CHECK(errno == EINVAL);
+    errno = 0;
+    CLI::detail::to_flag_value(
+        "77777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777");
+    CHECK(errno == ERANGE);
+    errno = 0;
     CHECK(-1 == CLI::detail::to_flag_value("NO"));
     CHECK(475555233 == CLI::detail::to_flag_value("475555233"));
 }
diff --git a/tests/fuzzFail/fuzz_file_fail1 b/tests/fuzzFail/fuzz_file_fail1
new file mode 100644
index 000000000..06b1c382f
--- /dev/null
+++ b/tests/fuzzFail/fuzz_file_fail1
@@ -0,0 +1 @@
+nflag2=555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555555"="