diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 32379e8..4324179 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -16,9 +16,12 @@ jobs:
 
         toolchain:
           - macos-latest-clang
+          - macos-12-clang
           - ubuntu-latest-clang
           - ubuntu-latest-gcc
+          - windows-2019-msvc
           - windows-latest-msvc
+          - windows-latest-clang
 
         include:
           - toolchain: macos-latest-clang
@@ -26,6 +29,11 @@ jobs:
             c_compiler: clang
             cxx_compiler: clang++
 
+          - toolchain: macos-12-clang
+            os: macos-latest
+            c_compiler: clang
+            cxx_compiler: clang++
+
           - toolchain: ubuntu-latest-clang
             os: ubuntu-latest
             c_compiler: clang
@@ -36,11 +44,22 @@ jobs:
             c_compiler: cc
             cxx_compiler: g++
 
+          - toolchain: windows-2019-msvc
+            os: windows-2019
+            c_compiler: msvc
+            cxx_compiler: msvc
+
           - toolchain: windows-latest-msvc
             os: windows-latest
             c_compiler: msvc
             cxx_compiler: msvc
 
+          - toolchain: windows-latest-clang
+            os: windows-latest
+            c_compiler: clang-cl
+            cxx_compiler: clang-cl
+            cmake_opts: -T ClangCL
+
     steps:
 
     - name: Checkout Code
@@ -48,7 +67,7 @@ jobs:
 
     - name: Configure
       working-directory: test
-      run: cmake -S . -B build
+      run: cmake -S . -B build ${{ matrix.cmake_opts }}
       env:
         CC: ${{ matrix.c_compiler }}
         CXX: ${{ matrix.cxx_compiler }}
diff --git a/include/argparse/argparse.hpp b/include/argparse/argparse.hpp
index 569704e..b88ac63 100644
--- a/include/argparse/argparse.hpp
+++ b/include/argparse/argparse.hpp
@@ -246,10 +246,10 @@ template <class T> struct parse_number<T> {
 
 namespace {
 
-template <class T> constexpr auto generic_strtod = nullptr;
-template <> constexpr auto generic_strtod<float> = strtof;
-template <> constexpr auto generic_strtod<double> = strtod;
-template <> constexpr auto generic_strtod<long double> = strtold;
+template <class T> inline const auto generic_strtod = nullptr;
+template <> inline const auto generic_strtod<float> = strtof;
+template <> inline const auto generic_strtod<double> = strtod;
+template <> inline const auto generic_strtod<long double> = strtold;
 
 } // namespace