diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index ef3b5f2..3850ad9 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -47,7 +47,7 @@ jobs:
           cmake -B build
           -DCMAKE_BUILD_TYPE=Debug
           -DCMAKE_CXX_STANDARD=23
-          -Dfrozen.tests=ON
+          "-Dfrozen.tests=ON"
           -DCMAKE_VERBOSE_MAKEFILE=ON
           ${{ matrix.cmake_args }}
 
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8c01481..fcffc18 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -22,6 +22,20 @@ include(CTest)
 include(GNUInstallDirs)
 include(cmake/detect_cxx_version.cmake)
 
+# ###################### sccache #######################
+find_program(SCCACHE_PROGRAM sccache)
+if(SCCACHE_PROGRAM)
+    message(STATUS "sccache found: ${SCCACHE_PROGRAM}")
+    set(CMAKE_C_COMPILER_LAUNCHER "${SCCACHE_PROGRAM}")
+    set(CMAKE_CXX_COMPILER_LAUNCHER "${SCCACHE_PROGRAM}")
+else()
+    message(STATUS "sccache not found; building without a compiler cache")
+endif()
+
+if(MSVC)
+    set(CMAKE_MSVC_DEBUG_INFORMATION_FORMAT "$<$<CONFIG:Debug,RelWithDebInfo>:Embedded>")
+endif()
+
 #
 # The `frozen.testing`, `frozen.benchmark`, and `frozen.coverage` options
 # only appear as cmake-gui and ccmake options iff frozen is the highest
diff --git a/include/frozen/algorithm.h b/include/frozen/algorithm.h
index ffcbcc9..a538f7c 100644
--- a/include/frozen/algorithm.h
+++ b/include/frozen/algorithm.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_LETITGO_ALGORITHM_H
-#define FROZEN_LETITGO_ALGORITHM_H
+#pragma once
 
 // Require C++23 or later
 #if defined(_MSVC_LANG)
@@ -270,5 +269,3 @@ namespace frozen
     }
 
 }  // namespace frozen
-
-#endif
diff --git a/include/frozen/bits/algorithms.h b/include/frozen/bits/algorithms.h
index 50d2eec..310c31d 100644
--- a/include/frozen/bits/algorithms.h
+++ b/include/frozen/bits/algorithms.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_LETITGO_BITS_ALGORITHMS_H
-#define FROZEN_LETITGO_BITS_ALGORITHMS_H
+#pragma once
 
 #include "frozen/bits/basic_types.h"
 
@@ -266,5 +265,3 @@ namespace frozen::bits
     }
 
 }  // namespace frozen::bits
-
-#endif
diff --git a/include/frozen/bits/basic_types.h b/include/frozen/bits/basic_types.h
index e1bf0d4..817908f 100644
--- a/include/frozen/bits/basic_types.h
+++ b/include/frozen/bits/basic_types.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_LETITGO_BASIC_TYPES_H
-#define FROZEN_LETITGO_BASIC_TYPES_H
+#pragma once
 
 #include "frozen/bits/constexpr_assert.h"
 #include "frozen/bits/exceptions.h"
@@ -247,5 +246,3 @@ namespace frozen::bits
     };
 
 }  // namespace frozen::bits
-
-#endif
diff --git a/include/frozen/bits/constexpr_assert.h b/include/frozen/bits/constexpr_assert.h
index 95543f3..d69c25f 100644
--- a/include/frozen/bits/constexpr_assert.h
+++ b/include/frozen/bits/constexpr_assert.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_LETITGO_CONSTEXPR_ASSERT_H
-#define FROZEN_LETITGO_CONSTEXPR_ASSERT_H
+#pragma once
 
 #include <cassert>
 #include <utility>
@@ -29,5 +28,3 @@
 inline void constexpr_assert_failed() {}
 
 #define constexpr_assert(cond, msg) ((void) ((cond) ? 0 : (constexpr_assert_failed(), 0)))
-
-#endif
diff --git a/include/frozen/bits/defines.h b/include/frozen/bits/defines.h
index d9aa2d1..c3f6740 100644
--- a/include/frozen/bits/defines.h
+++ b/include/frozen/bits/defines.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_LETITGO_DEFINES_H
-#define FROZEN_LETITGO_DEFINES_H
+#pragma once
 
 // C++23 guarantees all previously-detected features:
 // - string_view (C++17)
@@ -31,5 +30,3 @@
 // The feature-detection macros have been removed. This header
 // is here only for backward compatibility to the original
 // frozen implementation.
-
-#endif  // FROZEN_LETITGO_DEFINES_H
diff --git a/include/frozen/bits/elsa.h b/include/frozen/bits/elsa.h
index c07ccfd..f26b3a9 100644
--- a/include/frozen/bits/elsa.h
+++ b/include/frozen/bits/elsa.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_LETITGO_ELSA_H
-#define FROZEN_LETITGO_ELSA_H
+#pragma once
 
 #include <concepts>
 #include <type_traits>
@@ -64,5 +63,3 @@ namespace frozen
     template <class T = void>
     using anna = elsa<T>;
 }  // namespace frozen
-
-#endif
diff --git a/include/frozen/bits/elsa_std.h b/include/frozen/bits/elsa_std.h
index 84bcad6..f2640f0 100644
--- a/include/frozen/bits/elsa_std.h
+++ b/include/frozen/bits/elsa_std.h
@@ -1,5 +1,4 @@
-#ifndef FROZEN_LETITGO_BITS_ELSA_STD_H
-#define FROZEN_LETITGO_BITS_ELSA_STD_H
+#pragma once
 
 #include "elsa.h"
 #include "hash_string.h"
@@ -39,5 +38,3 @@ namespace frozen
     };
 
 }  // namespace frozen
-
-#endif  // FROZEN_LETITGO_BITS_ELSA_STD_H
diff --git a/include/frozen/bits/exceptions.h b/include/frozen/bits/exceptions.h
index 9c71346..86db84f 100644
--- a/include/frozen/bits/exceptions.h
+++ b/include/frozen/bits/exceptions.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_LETITGO_EXCEPTIONS_H
-#define FROZEN_LETITGO_EXCEPTIONS_H
+#pragma once
 
 #if defined(FROZEN_NO_EXCEPTIONS) || (defined(_MSC_VER) && !defined(_CPPUNWIND)) || \
     (!defined(_MSC_VER) && !defined(__cpp_exceptions))
@@ -35,5 +34,3 @@
     #define FROZEN_THROW_OR_ABORT(err) throw err
 
 #endif
-
-#endif
diff --git a/include/frozen/bits/hash_string.h b/include/frozen/bits/hash_string.h
index 43ee83c..f35ecbb 100644
--- a/include/frozen/bits/hash_string.h
+++ b/include/frozen/bits/hash_string.h
@@ -1,18 +1,27 @@
-#ifndef FROZEN_LETITGO_BITS_HASH_STRING_H
-#define FROZEN_LETITGO_BITS_HASH_STRING_H
+#pragma once
 
 #include <cstddef>
 
 namespace frozen
 {
+    // djb2 hash constants
+    constexpr std::size_t djb2_initial = 5381;
+    constexpr std::size_t djb2_multiplier = 33;
+
+    // FNV-1 hash constants (32-bit)
+    constexpr std::size_t fnv_offset_basis = 0x811c9dc5;
+    constexpr std::size_t fnv_prime = 0x01000193;
+    constexpr std::size_t fnv_shift_bits = 8;
 
     template <typename String>
     constexpr std::size_t hash_string(const String& value)
     {
-        std::size_t d = 5381;
-        for (const auto& c: value)
-            d = d * 33 + static_cast<std::size_t>(c);
-        return d;
+        std::size_t hash = djb2_initial;
+        for (const auto& chr: value)
+        {
+            hash = (hash * djb2_multiplier) + static_cast<std::size_t>(chr);
+        }
+        return hash;
     }
 
     // https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
@@ -20,12 +29,12 @@ namespace frozen
     template <typename String>
     constexpr std::size_t hash_string(const String& value, std::size_t seed)
     {
-        std::size_t d = (0x811c9dc5 ^ seed) * static_cast<std::size_t>(0x01000193);
-        for (const auto& c: value)
-            d = (d ^ static_cast<std::size_t>(c)) * static_cast<std::size_t>(0x01000193);
-        return d >> 8;
+        std::size_t hash = (fnv_offset_basis ^ seed) * static_cast<std::size_t>(fnv_prime);
+        for (const auto& chr: value)
+        {
+            hash = (hash ^ static_cast<std::size_t>(chr)) * static_cast<std::size_t>(fnv_prime);
+        }
+        return hash >> fnv_shift_bits;
     }
 
 }  // namespace frozen
-
-#endif  // FROZEN_LETITGO_BITS_HASH_STRING_H
diff --git a/include/frozen/bits/mpl.h b/include/frozen/bits/mpl.h
index 1f405b2..7f0d808 100644
--- a/include/frozen/bits/mpl.h
+++ b/include/frozen/bits/mpl.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_LETITGO_BITS_MPL_H
-#define FROZEN_LETITGO_BITS_MPL_H
+#pragma once
 
 #include <utility>
 
@@ -53,5 +52,3 @@ namespace frozen::bits
     using remove_cv_t = typename remove_cv<T>::type;
 
 }  // namespace frozen::bits
-
-#endif
diff --git a/include/frozen/bits/pmh.h b/include/frozen/bits/pmh.h
index e7864be..7591886 100644
--- a/include/frozen/bits/pmh.h
+++ b/include/frozen/bits/pmh.h
@@ -21,13 +21,11 @@
  */
 
 // inspired from http://stevehanov.ca/blog/index.php?id=119
-#ifndef FROZEN_LETITGO_PMH_H
-#define FROZEN_LETITGO_PMH_H
+#pragma once
 
 #include "frozen/bits/algorithms.h"
 #include "frozen/bits/basic_types.h"
 
-#include <array>
 #include <cstddef>
 #include <cstdint>
 #include <limits>
@@ -282,5 +280,3 @@ namespace frozen::bits
     }
 
 }  // namespace frozen::bits
-
-#endif
diff --git a/include/frozen/bits/version.h b/include/frozen/bits/version.h
index cc6f1e7..a6278df 100644
--- a/include/frozen/bits/version.h
+++ b/include/frozen/bits/version.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_LETITGO_VERSION_H
-#define FROZEN_LETITGO_VERSION_H
+#pragma once
 
 // Require C++23 or later
 #if defined(_MSVC_LANG)
@@ -35,5 +34,3 @@
 #define FROZEN_MAJOR_VERSION 2
 #define FROZEN_MINOR_VERSION 0
 #define FROZEN_PATCH_VERSION 0
-
-#endif
diff --git a/include/frozen/map.h b/include/frozen/map.h
index dc203c9..733b51a 100644
--- a/include/frozen/map.h
+++ b/include/frozen/map.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_LETITGO_MAP_H
-#define FROZEN_LETITGO_MAP_H
+#pragma once
 
 // Require C++23 or later
 #if defined(_MSVC_LANG)
@@ -38,6 +37,7 @@
 #include "frozen/bits/mpl.h"
 #include "frozen/bits/version.h"
 
+#include <functional>
 #include <iterator>
 #include <utility>
 
@@ -456,5 +456,3 @@ namespace frozen
     }
 
 }  // namespace frozen
-
-#endif
diff --git a/include/frozen/random.h b/include/frozen/random.h
index 5a57c35..1d41232 100644
--- a/include/frozen/random.h
+++ b/include/frozen/random.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_LETITGO_RANDOM_H
-#define FROZEN_LETITGO_RANDOM_H
+#pragma once
 
 // Require C++23 or later
 #if defined(_MSVC_LANG)
@@ -104,5 +103,3 @@ namespace frozen
     using default_prg_t = minstd_rand;
 
 }  // namespace frozen
-
-#endif
diff --git a/include/frozen/set.h b/include/frozen/set.h
index 184e202..2ee4195 100644
--- a/include/frozen/set.h
+++ b/include/frozen/set.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_SET_H
-#define FROZEN_SET_H
+#pragma once
 
 // Require C++23 or later
 #if defined(_MSVC_LANG)
@@ -36,6 +35,7 @@
 #include "frozen/bits/basic_types.h"
 #include "frozen/bits/version.h"
 
+#include <functional>
 #include <iterator>
 #include <utility>
 
@@ -315,5 +315,3 @@ namespace frozen
     set(T, Args...) -> set<T, sizeof...(Args) + 1>;
 
 }  // namespace frozen
-
-#endif
diff --git a/include/frozen/string.h b/include/frozen/string.h
index 560fc6f..71ad52d 100644
--- a/include/frozen/string.h
+++ b/include/frozen/string.h
@@ -1,21 +1,8 @@
-#ifndef FROZEN_LETITGO_STRING_H
-#define FROZEN_LETITGO_STRING_H
-
-// Require C++23 or later
-#if defined(_MSVC_LANG)
-    #if _MSVC_LANG < 202302L
-        #error "frozen/string.h requires C++23 or later. Compile with /std:c++latest or /std:c++23."
-    #endif
-#elif __cplusplus < 202302L
-    #error "frozen/string.h requires C++23 or later. Compile with -std=c++23 or later."
-#endif
-
-#include "frozen/bits/elsa.h"
-#include "frozen/bits/hash_string.h"
+#pragma once
+
 #include "frozen/bits/version.h"
 
 #include <cstddef>
-#include <functional>
 #include <string_view>
 
 namespace frozen
@@ -58,5 +45,3 @@ namespace frozen
     }  // namespace string_literals
 
 }  // namespace frozen
-
-#endif
diff --git a/include/frozen/unordered_map.h b/include/frozen/unordered_map.h
index 4fadde8..cacea20 100644
--- a/include/frozen/unordered_map.h
+++ b/include/frozen/unordered_map.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_LETITGO_UNORDERED_MAP_H
-#define FROZEN_LETITGO_UNORDERED_MAP_H
+#pragma once
 
 // Require C++23 or later
 #if defined(_MSVC_LANG)
@@ -253,5 +252,3 @@ namespace frozen
     }
 
 }  // namespace frozen
-
-#endif
diff --git a/include/frozen/unordered_set.h b/include/frozen/unordered_set.h
index 5d7236f..4d19112 100644
--- a/include/frozen/unordered_set.h
+++ b/include/frozen/unordered_set.h
@@ -20,8 +20,7 @@
  * under the License.
  */
 
-#ifndef FROZEN_LETITGO_UNORDERED_SET_H
-#define FROZEN_LETITGO_UNORDERED_SET_H
+#pragma once
 
 // Require C++23 or later
 #if defined(_MSVC_LANG)
@@ -39,6 +38,7 @@
 #include "frozen/bits/version.h"
 #include "frozen/random.h"
 
+#include <functional>
 #include <utility>
 
 namespace frozen
@@ -211,5 +211,3 @@ namespace frozen
     unordered_set(T, Args...) -> unordered_set<T, sizeof...(Args) + 1>;
 
 }  // namespace frozen
-
-#endif
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 60a439a..5f0f3b0 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -25,7 +25,7 @@ target_sources(frozen.tests PRIVATE
 
 string(CONCAT generator
   # msvc gives invalid integral overflow warning for unsigned type
-  "$<$<CXX_COMPILER_ID:MSVC>:/W3;/WX;/wd4307>"
+  "$<$<CXX_COMPILER_ID:MSVC>:/W3;/WX;/wd4307;/wd4018>"
   "$<$<OR:$<CXX_COMPILER_ID:GNU>"
         ",$<CXX_COMPILER_ID:Clang>"
         ",$<CXX_COMPILER_ID:AppleClang>>"
@@ -57,4 +57,4 @@ target_compile_options(test_no_expections PUBLIC
   $<$<NOT:$<CXX_COMPILER_ID:MSVC>>:-fno-exceptions>)
 
 add_test(no_exceptions test_no_expections)
-set_tests_properties(no_exceptions PROPERTIES WILL_FAIL TRUE)
+set_tests_properties(no_exceptions PROPERTIES WILL_FAIL TRUE TIMEOUT 10)
diff --git a/tests/no_exceptions.cpp b/tests/no_exceptions.cpp
index fd5e0b0..2db89b2 100644
--- a/tests/no_exceptions.cpp
+++ b/tests/no_exceptions.cpp
@@ -3,6 +3,10 @@
 #include <csignal>
 #include <cstdlib>
 
+#ifdef _MSC_VER
+    #include <crtdbg.h>
+#endif
+
 // https://discourse.cmake.org/t/tests-that-are-meant-to-abort/537/3
 // This is a hack to implement death tests in CTest.
 extern "C" void error_test_handle_abort(int)
@@ -12,7 +16,17 @@ extern "C" void error_test_handle_abort(int)
 
 struct test_override_abort
 {
-    test_override_abort() noexcept { std::signal(SIGABRT, error_test_handle_abort); }
+    test_override_abort() noexcept
+    {
+#ifdef _MSC_VER
+        // Prevent abort() from showing a dialog or invoking Windows Error
+        // Reporting — either of which hangs headless CI environments.
+        _set_abort_behavior(0, _WRITE_ABORT_MSG | _CALL_REPORTFAULT);
+        _CrtSetReportMode(_CRT_ASSERT, _CRTDBG_MODE_DEBUG);
+        _CrtSetReportMode(_CRT_ERROR, _CRTDBG_MODE_DEBUG);
+#endif
+        std::signal(SIGABRT, error_test_handle_abort);
+    }
 };
 
 test_override_abort handler {};