diff --git a/include/fast_float/float_common.h b/include/fast_float/float_common.h
index 77e3e59..468458d 100644
--- a/include/fast_float/float_common.h
+++ b/include/fast_float/float_common.h
@@ -122,8 +122,10 @@
     && FASTFLOAT_HAS_BIT_CAST \
     && __cpp_lib_constexpr_algorithms >= 201806L /*For std::copy and std::fill*/
 #define FASTFLOAT_CONSTEXPR20 constexpr
+#define FASTFLOAT_IS_CONSTEXPR 1
 #else
 #define FASTFLOAT_CONSTEXPR20
+#define FASTFLOAT_IS_CONSTEXPR 0
 #endif
 
 namespace fast_float {
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 223c9e1..2dc784e 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -60,7 +60,13 @@ fast_float_add_cpp_test(rcppfastfloat_test)
 fast_float_add_cpp_test(example_test)
 fast_float_add_cpp_test(example_comma_test)
 fast_float_add_cpp_test(basictest)
-target_compile_features(basictest PRIVATE cxx_std_17)
+option(FASTFLOAT_CONSTEXPR_TESTS "Constexpr tests" OFF)
+if (FASTFLOAT_CONSTEXPR_TESTS)
+  target_compile_features(basictest PRIVATE cxx_std_20)
+  target_compile_definitions(basictest PRIVATE FASTFLOAT_CONSTEXPR_TESTS)
+else()
+  target_compile_features(basictest PRIVATE cxx_std_17)
+endif()
 
 fast_float_add_cpp_test(long_test)
 fast_float_add_cpp_test(powersoffive_hardround)
diff --git a/tests/basictest.cpp b/tests/basictest.cpp
index 433a9b5..4fe391f 100644
--- a/tests/basictest.cpp
+++ b/tests/basictest.cpp
@@ -10,6 +10,7 @@
 #include <limits>
 #include <string>
 #include <system_error>
+#include <type_traits>
 #include <cfenv>
 
 #ifndef SUPPLEMENTAL_TEST_DATA_DIR
@@ -614,7 +615,44 @@ void basic_test(float val) {
   }
 }
 
+namespace {
+template <int>
+struct dummy {};
+
+template <auto val>
+struct verify_error;
+} //anonymous namespace
+
+#if defined(FASTFLOAT_CONSTEXPR_TESTS)
+#if !FASTFLOAT_IS_CONSTEXPR
+#error "from_chars must be constexpr for constexpr tests"
+#endif
+
+// Add constexpr testing to verify when the arguments are constant expressions
+#define verify(lhs, rhs)                                                       \
+  {                                                                            \
+    INFO(lhs);                                                                 \
+    basic_test(lhs, rhs);                                                      \
+    [&]<typename T>() {                                                        \
+      if constexpr (requires {                                                 \
+        typename ::dummy<(T(lhs), 0)>;                                         \
+        typename ::dummy<((void)(rhs), 0)>;                                    \
+      }) {                                                                     \
+        constexpr auto sv = T(lhs);                                            \
+        constexpr auto val = [&] {                                             \
+          ::std::remove_cvref_t<decltype(rhs)> ret;                            \
+          (void)::fast_float::from_chars(sv.data(), sv.data() + sv.size(),     \
+                                         ret);                                 \
+          return ret;                                                          \
+        }();                                                                   \
+        static_assert(val == (rhs));                                           \
+      }                                                                        \
+    }.operator()<::std::string_view>();                                        \
+  }
+#else
 #define verify(lhs, rhs) { INFO(lhs); basic_test(lhs, rhs); }
+#endif
+
 #define verify32(val) { INFO(#val); basic_test(val); }
 
 #define verify_options(lhs, rhs) { INFO(lhs); basic_test(lhs, rhs, options); }