diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d6958b90..6377732b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -166,13 +166,13 @@ jobs:
             echo "===== parallel jobs: $jobs"
             parallel -kv --lb 'cd build/extra/{} && bash ../../../../misc/testsuite/mimic_ctest.sh' ::: $jobs
           fi
-      - name: Run file system test suite
+      - name: Run file system tests
         run: |
           jobs="gcc/debug gcc/release clang/debug clang/release"
           test "${{ matrix.use_extra }}" = "true" && jobs="$jobs gcc-m32/debug gcc-m32/release"
           echo "===== parallel jobs: $jobs"
           parallel -kv --lb 'cd build/extra/{} && bash ../../../../misc/testsuite/test_symlinks.sh' ::: $jobs
-      - name: Run file system test suite with Valgrind
+      - name: Run file system tests with Valgrind
         if: false # note: valgrind is SLOW
         run: |
           if command -v valgrind >/dev/null; then
@@ -237,6 +237,7 @@ jobs:
       - name: Check out test suite
         if: ${{ matrix.testsuite }}
         run: git clone --depth=1 https://github.com/upx/upx-testsuite ../deps/upx-testsuite
+      - run: set -x; xcode-select -p || true; xcodebuild -version || true
       - run: set -x; clang --version; clang++ --version
       - run: clang   -E -x c   -dM /dev/null # list predefined macros for C
       - run: clang++ -E -x c++ -dM /dev/null # list predefined macros for C++
@@ -283,7 +284,7 @@ jobs:
           test -n "${{ matrix.gcc }}" && jobs="$jobs gcc/debug gcc/release"
           echo "===== parallel jobs: $jobs"
           parallel -kv --lb 'cd build/extra/{} && bash ../../../../misc/testsuite/mimic_ctest.sh' ::: $jobs
-      - name: Run file system test suite
+      - name: Run file system tests
         if: ${{ matrix.testsuite }} # for coreutils readlink
         run: |
           export PATH="$HOMEBREW_PREFIX/opt/coreutils/libexec/gnubin:$PATH"
@@ -615,7 +616,7 @@ jobs:
           jobs="${ZIG_TARGET}${ZIG_PIC}/debug ${ZIG_TARGET}${ZIG_PIC}/release"
           echo "===== parallel jobs: $jobs"
           parallel -kv --lb 'cd build/zig/{} && bash ../../../../misc/testsuite/mimic_ctest.sh' ::: $jobs
-      - name: Run file system test suite
+      - name: Run file system tests
         if: ${{ matrix.zig_target == 'i386-linux-musl' || matrix.zig_target == 'x86_64-linux-musl' || matrix.zig_target == 'x86_64-linux-gnu.2.3.4' }}
         run: |
           apk add coreutils sudo
diff --git a/src/bele_policy.h b/src/bele_policy.h
index f125bf44..9cc60c0e 100644
--- a/src/bele_policy.h
+++ b/src/bele_policy.h
@@ -49,7 +49,7 @@
 
 #if defined(BELE_RTP)
 struct AbstractPolicy {
-    explicit inline AbstractPolicy() noexcept {}
+    explicit inline AbstractPolicy() noexcept = default;
     virtual inline ~AbstractPolicy() noexcept {}
     V bool isBE() C = 0;
     V bool isLE() C = 0;
@@ -97,7 +97,7 @@ struct BEPolicy final
     : public AbstractPolicy
 #endif
 {
-    explicit inline BEPolicy() noexcept {}
+    explicit inline BEPolicy() noexcept = default;
 #if defined(BELE_CTP)
     typedef N_BELE_RTP::BEPolicy RTP_Policy;
 #elif defined(BELE_RTP)
@@ -156,7 +156,7 @@ struct LEPolicy final
     : public AbstractPolicy
 #endif
 {
-    explicit inline LEPolicy() noexcept {}
+    explicit inline LEPolicy() noexcept = default;
 #if defined(BELE_CTP)
     typedef N_BELE_RTP::LEPolicy RTP_Policy;
 #elif defined(BELE_RTP)
diff --git a/src/check/dt_impl.cpp b/src/check/dt_impl.cpp
index 4bce6662..c93ab5d9 100644
--- a/src/check/dt_impl.cpp
+++ b/src/check/dt_impl.cpp
@@ -59,6 +59,10 @@
 // warning: comparison with NaN always evaluates to false in fast floating point modes
 #pragma clang diagnostic ignored "-Wtautological-constant-compare"
 #endif
+#if defined(__FAST_MATH__) && defined(__clang__) && (__clang_major__ + 0 >= 18)
+// warning: use of NaN is undefined behavior due to the currently enabled floating-point options
+#pragma clang diagnostic ignored "-Wnan-infinity-disabled"
+#endif
 
 #include <doctest/doctest/parts/doctest.cpp>
 
diff --git a/src/conf.h b/src/conf.h
index 6f00efdb..8b549a52 100644
--- a/src/conf.h
+++ b/src/conf.h
@@ -1,4 +1,4 @@
-/* conf.h --
+/* conf.h -- primary configuration
 
    This file is part of the UPX executable compressor.
 
@@ -32,6 +32,7 @@
 **************************************************************************/
 
 #include "util/system_headers.h"
+#include "util/system_undefs.h"
 #include "version.h"
 
 #if !defined(__has_attribute)
@@ -47,6 +48,7 @@
 // reserve name "upx" for namespace
 namespace upx {}
 
+// check compiler core
 static_assert(CHAR_BIT == 8);
 static_assert(sizeof(short) == 2);
 static_assert(sizeof(int) == 4);
@@ -58,7 +60,7 @@ static_assert((1u << 31) << 1 == 0);
 static_assert(((int) (1u << 31)) >> 31 == -1); // arithmetic right shift
 static_assert((-1) >> 31 == -1);               // arithmetic right shift
 static_assert(CHAR_MAX == 255);                // -funsigned-char
-static_assert((char) (-1) == 255);
+static_assert((char) (-1) == 255);             // -funsigned-char
 
 // enable some more strict warnings for Git developer builds
 #if defined(UPX_CONFIG_DISABLE_WSTRICT) && (UPX_CONFIG_DISABLE_WSTRICT + 0 == 0)
@@ -215,20 +217,6 @@ typedef upx_int64_t upx_off_t;
 // portab
 **************************************************************************/
 
-// some platform system headers may pre-define these, so undef to avoid conflicts
-#undef _
-#undef __
-#undef ___
-#undef dos
-#undef large
-#undef linux
-#undef PAGE_MASK
-#undef PAGE_SIZE
-#undef small
-#undef SP
-#undef SS
-#undef tos
-#undef unix
 #if (ACC_OS_POSIX) && !defined(__unix__)
 #define __unix__ 1
 #endif
diff --git a/src/main.cpp b/src/main.cpp
index b9c0aa77..ab67e456 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,4 +1,4 @@
-/* main.cpp --
+/* main.cpp -- main entry
 
    This file is part of the UPX executable compressor.
 
diff --git a/src/util/system_headers.h b/src/util/system_headers.h
index 4b7f1d30..5f3aa93d 100644
--- a/src/util/system_headers.h
+++ b/src/util/system_headers.h
@@ -40,8 +40,15 @@
 #if defined(__CYGWIN64__) && !defined(__CYGWIN__)
 #error "missing __CYGWIN__"
 #endif
-#if defined(__clang__) || defined(__GNUC__)
+#if defined(__MINGW64__) && !defined(__MINGW32__)
+#error "missing __MINGW32__"
+#endif
+#if defined(_WIN64) && !defined(_WIN32)
+#error "missing _WIN32"
+#endif
+
 // byte order - these are pre-defined since gcc-4.6 (2011) and clang-3.2 (2012)
+#if defined(__clang__) || defined(__GNUC__)
 #if !defined(__ORDER_BIG_ENDIAN__) || (__ORDER_BIG_ENDIAN__ + 0 == 0)
 #error "missing __ORDER_BIG_ENDIAN__"
 #endif
@@ -61,6 +68,7 @@
 #error "unexpected __BYTE_ORDER__"
 #endif
 #endif
+
 // pic and pie
 #if defined(__PIC__) && defined(__pic__)
 static_assert((__PIC__) == (__pic__));
diff --git a/src/util/system_undefs.h b/src/util/system_undefs.h
new file mode 100644
index 00000000..b54bf45b
--- /dev/null
+++ b/src/util/system_undefs.h
@@ -0,0 +1,58 @@
+/* system_undefs.h -- undef system pre-defines
+
+   This file is part of the UPX executable compressor.
+
+   Copyright (C) 1996-2024 Markus Franz Xaver Johannes Oberhumer
+   All Rights Reserved.
+
+   UPX and the UCL library are free software; you can redistribute them
+   and/or modify them under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2 of
+   the License, or (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; see the file COPYING.
+   If not, write to the Free Software Foundation, Inc.,
+   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+   Markus F.X.J. Oberhumer
+   <markus@oberhumer.com>
+ */
+
+// some platform system headers may pre-define these, so undef to avoid conflicts
+#undef _
+#undef __
+#undef ___
+#undef ____
+#undef _____
+#undef MIPSEB
+#undef MIPSEL
+#undef PAGE_MASK
+#undef PAGE_SIZE
+#undef PPC
+#undef R3000
+#undef R4000
+#undef SP
+#undef SS
+#undef WIN32
+#undef WIN64
+#undef WINNT
+#undef dos
+#undef far
+#undef huge
+#undef i386
+#undef large
+#undef linux
+#undef mips
+#undef near
+#undef powerpc
+#undef small
+#undef tos
+#undef unix
+
+/* vim:set ts=4 sw=4 et: */
diff --git a/src/work.cpp b/src/work.cpp
index 3f4bf6c1..12e801fa 100644
--- a/src/work.cpp
+++ b/src/work.cpp
@@ -1,4 +1,4 @@
-/* work.cpp -- main driver
+/* work.cpp -- main work driver
 
    This file is part of the UPX executable compressor.
 
@@ -26,12 +26,12 @@
  */
 
 // This file implements the central loop, and it uses class PackMaster to
-// dispatch. PackMaster by itself will instantiate a concrete subclass
-// of class PackerBase which then does the actual work.
+// dispatch. PackMaster by itself will instantiate a concrete subclass of
+// class PackerBase which then does the actual work; search for "HERE".
 // And see p_com.cpp for a simple executable format.
 //
-// And this file also has the burden to deal with all those pesky low-level
-// file handling issues.
+// Additionally this file also has the burden to deal with all those pesky
+// low-level file handling issues.
 
 #define WANT_WINDOWS_LEAN_H 1 // _get_osfhandle, GetFileTime, SetFileTime
 #include "util/system_headers.h"