diff --git a/.travis.yml b/.travis.yml
index 0e575a6..b202748 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -30,6 +30,6 @@ addons:
       - "libqt5charts5-dev"
 
 script:
-  - "qmake test/tstcpputils.pro"
+  - "qmake CLONE_EXPECTED=1 CLONE_FMT=1 test/tstcpputils.pro"
   - "make -j2"
   - ./tstcpputils
diff --git a/CMakeLists.txt b/CMakeLists.txt
index aff08d1..7b3aaa8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -19,6 +19,8 @@ set(sources
 )
 
 set(dependencies
+    expected
+    fmt
 )
 
 idf_component_register(
diff --git a/src/cpptypesafeenum.h b/src/cpptypesafeenum.h
index 303c193..9d93c01 100644
--- a/src/cpptypesafeenum.h
+++ b/src/cpptypesafeenum.h
@@ -1,15 +1,16 @@
 #pragma once
 
 // system includes
-#include <optional>
 #include <string>
 
+// 3rdparty lib includes
+#include <tl/expected.hpp>
+#include <fmt/core.h>
+
 // local includes
 #include "cppmacros.h"
 
-#define CPPTYPESAFEENUM_SHOULD_INLINE
-
-// These two macros make it possible to define a typesafe enum with parse and
+// These macros make it possible to define a typesafe enum with parse and
 // toString methods
 
 #define DECLARE_TYPESAFE_ENUM_HELPER1(name) name,
@@ -17,7 +18,6 @@
 #define DECLARE_TYPESAFE_ENUM_HELPER3(name) else if (str == CPP_STRINGIFY(name)) return TheEnum::name;
 #define DECLARE_TYPESAFE_ENUM_HELPER4(name) cb(TheEnum::name, CPP_STRINGIFY(name));
 
-#ifdef CPPTYPESAFEENUM_SHOULD_INLINE
 #define DECLARE_TYPESAFE_ENUM(Name, Derivation, Values) \
     enum class Name Derivation \
     { \
@@ -30,14 +30,14 @@
         using TheEnum = Name; \
         Values(DECLARE_TYPESAFE_ENUM_HELPER2) \
         } \
-        return std::string{"Unknown " #Name "("} + std::to_string(int(value)) + ')'; \
+        return fmt::format("Unknown " #Name "({})", int(value)); \
     } \
-    inline std::optional<Name> parse##Name(std::string_view str) \
+    inline tl::expected<Name, std::string> parse##Name(std::string_view str) \
     { \
         using TheEnum = Name; \
         if (false) {} \
         Values(DECLARE_TYPESAFE_ENUM_HELPER3) \
-        return std::nullopt; \
+        return tl::make_unexpected(fmt::format("invalid " #Name " ({})", str)); \
     } \
     template<typename T> \
     void iterate##Name(T &&cb) \
@@ -47,36 +47,3 @@
     }
 
 #define IMPLEMENT_TYPESAFE_ENUM(Name, Derivation, Values)
-#else
-#define DECLARE_TYPESAFE_ENUM(Name, Derivation, Values) \
-    enum class Name Derivation \
-    { \
-        Values(DECLARE_TYPESAFE_ENUM_HELPER1) \
-    }; \
-    std::string toString(Name value); \
-    std::optional<Name> parse##Name(std::string_view str); \
-    template<typename T> \
-    void iterate##Name(T &&cb) \
-    { \
-        using TheEnum = Name; \
-        Values(DECLARE_TYPESAFE_ENUM_HELPER4) \
-    }
-
-#define IMPLEMENT_TYPESAFE_ENUM(Name, Derivation, Values) \
-    ExportPrefix std::string toString(Name value) \
-    { \
-        switch (value) \
-        { \
-        using TheEnum = Name; \
-        Values(DECLARE_TYPESAFE_ENUM_HELPER2) \
-        } \
-        return std::string{"Unknown " #Name "("} + std::to_string(int(value)) + ')'; \
-    } \
-    ExportPrefix std::optional<Name> parse##Name(std::string_view str) \
-    { \
-        using TheEnum = Name; \
-        if (false) {} \
-        Values(DECLARE_TYPESAFE_ENUM_HELPER3) \
-        return std::nullopt; \
-    }
-#endif
diff --git a/src/numberparsing.h b/src/numberparsing.h
index 869bfb7..c25f51a 100644
--- a/src/numberparsing.h
+++ b/src/numberparsing.h
@@ -2,74 +2,78 @@
 
 // system includes
 #include <cstdint>
-#include <optional>
 #include <cstdio>
 #include <inttypes.h>
+#include <string>
+
+// 3rdparty lib includes
+#include <tl/expected.hpp>
+#include <fmt/format.h>
 
 namespace cpputils {
-template<typename T> constexpr std::optional<T> fromString(std::string_view str) = delete;
+template<typename T> constexpr tl::expected<T, std::string> fromString(std::string_view str) = delete;
 
-template<> constexpr inline std::optional<int8_t> fromString<int8_t>(std::string_view str)
+template<> constexpr inline tl::expected<int8_t, std::string> fromString<int8_t>(std::string_view str)
 {
     int8_t val{};
-    if (std::sscanf(str.data(), "%" SCNi8, &val) == 1)
-        return val;
-    return std::nullopt;
+    if (std::sscanf(str.data(), "%" SCNi8, &val) != 1)
+        return tl::make_unexpected(fmt::format("invalid int8_t {}", str));
+    return val;
 }
 
-template<> constexpr inline std::optional<uint8_t> fromString<uint8_t>(std::string_view str)
+template<> constexpr inline tl::expected<uint8_t, std::string> fromString<uint8_t>(std::string_view str)
 {
     uint8_t val{};
-    if (std::sscanf(str.data(), "%" SCNu8, &val) == 1)
-        return val;
-    return std::nullopt;
+    if (std::sscanf(str.data(), "%" SCNu8, &val) != 1)
+        return tl::make_unexpected(fmt::format("invalid uint8_t {}", str));
+    return val;
 }
 
-template<> constexpr inline std::optional<int16_t> fromString<int16_t>(std::string_view str)
+template<> constexpr inline tl::expected<int16_t, std::string> fromString<int16_t>(std::string_view str)
 {
     int16_t val{};
-    if (std::sscanf(str.data(), "%" SCNi16, &val) == 1)
-        return val;
-    return std::nullopt;
+    if (std::sscanf(str.data(), "%" SCNi16, &val) != 1)
+        return tl::make_unexpected(fmt::format("invalid int16_t {}", str));
+    return val;
 }
 
-template<> constexpr inline std::optional<uint16_t> fromString<uint16_t>(std::string_view str)
+template<> constexpr inline tl::expected<uint16_t, std::string> fromString<uint16_t>(std::string_view str)
 {
     uint16_t val{};
-    if (std::sscanf(str.data(), "%" SCNu16, &val) == 1)
-        return val;
-    return std::nullopt;
+    if (std::sscanf(str.data(), "%" SCNu16, &val) != 1)
+        return tl::make_unexpected(fmt::format("invalid uint16_t {}", str));
+    return val;
 }
 
-template<> constexpr inline std::optional<int32_t> fromString<int32_t>(std::string_view str)
+template<> constexpr inline tl::expected<int32_t, std::string> fromString<int32_t>(std::string_view str)
 {
     int32_t val{};
-    if (std::sscanf(str.data(), "%" SCNi32, &val) == 1)
-        return val;
-    return std::nullopt;
+    if (std::sscanf(str.data(), "%" SCNi32, &val) != 1)
+        return tl::make_unexpected(fmt::format("invalid int32_t {}", str));
+    return val;
 }
 
-template<> constexpr inline std::optional<uint32_t> fromString<uint32_t>(std::string_view str)
+template<> constexpr inline tl::expected<uint32_t, std::string> fromString<uint32_t>(std::string_view str)
 {
     uint32_t val{};
-    if (std::sscanf(str.data(), "%" SCNu32, &val) == 1)
-        return val;
-    return std::nullopt;
+    if (std::sscanf(str.data(), "%" SCNu32, &val) != 1)
+        return tl::make_unexpected(fmt::format("invalid uint32_t {}", str));
+    return val;
 }
 
-template<> constexpr inline std::optional<int64_t> fromString<int64_t>(std::string_view str)
+template<> constexpr inline tl::expected<int64_t, std::string> fromString<int64_t>(std::string_view str)
 {
     int64_t val{};
-    if (std::sscanf(str.data(), "%" SCNi64, &val) == 1)
-        return val;
-    return std::nullopt;
+    if (std::sscanf(str.data(), "%" SCNi64, &val) != 1)
+        return tl::make_unexpected(fmt::format("invalid int64_t {}", str));
+    return val;
 }
 
-template<> constexpr inline std::optional<uint64_t> fromString<uint64_t>(std::string_view str)
+template<> constexpr inline tl::expected<uint64_t, std::string> fromString<uint64_t>(std::string_view str)
 {
     uint64_t val{};
-    if (std::sscanf(str.data(), "%" SCNu64, &val) == 1)
-        return val;
-    return std::nullopt;
+    if (std::sscanf(str.data(), "%" SCNu64, &val) != 1)
+        return tl::make_unexpected(fmt::format("invalid uint64_t {}", str));
+    return val;
 }
 } // namespace cpputils
diff --git a/test/.gitignore b/test/.gitignore
index a222802..ef25983 100644
--- a/test/.gitignore
+++ b/test/.gitignore
@@ -1 +1,3 @@
 *.user*
+expected/
+fmt/
diff --git a/test/tstcpputils.pro b/test/tstcpputils.pro
index 6b6ca39..64bd781 100644
--- a/test/tstcpputils.pro
+++ b/test/tstcpputils.pro
@@ -6,7 +6,8 @@ QT -= gui widgets
 CONFIG += c++17 qt console warn_on depend_includepath testcase
 CONFIG -= app_bundle
 
-SOURCES += tst_cppbitmask.cpp
+SOURCES += \
+    tst_cppbitmask.cpp
 
 CPPUTILS_DIR = $$PWD/..
 
@@ -15,4 +16,39 @@ include($$CPPUTILS_DIR/cpputils_src.pri)
 include($$CPPUTILS_DIR/test/cpputilstestutils.pri)
 include($$CPPUTILS_DIR/test/cpputilstestutils_src.pri)
 
+equals(CLONE_EXPECTED, 1) {
+    EXPECTED_DIR = $$PWD/expected
+
+    message("Checking out expected...")
+    exists($$EXPECTED_DIR/.git): {
+        system("git -C $$EXPECTED_DIR pull")
+    } else {
+        system("git clone https://github.com/0xFEEDC0DE64/expected.git $$EXPECTED_DIR")
+    }
+} else: exists($$PWD/../../expected/include) {
+    EXPECTED_DIR = $$PWD/../../expected
+} else {
+    error("expected not found, please run git submodule update --init")
+}
+
+include($$EXPECTED_DIR/expected.pri)
+
+equals(CLONE_FMT, 1) {
+    FMT_DIR = $$PWD/fmt
+
+    message("Checking out fmt...")
+    exists($$FMT_DIR/.git): {
+        system("git -C $$FMT_DIR pull")
+    } else {
+        system("git clone https://github.com/0xFEEDC0DE64/fmt.git $$FMT_DIR")
+    }
+} else: exists($$PWD/../../fmt/include) {
+    FMT_DIR = $$PWD/../../fmt
+} else {
+    error("fmt not found, please run git submodule update --init")
+}
+
+include($$FMT_DIR/fmt.pri)
+include($$FMT_DIR/fmt_src.pri)
+
 QMAKE_CXXFLAGS += -Wno-missing-field-initializers