diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1542d3df..73937e4d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -378,8 +378,8 @@ jobs:
           - { zig_target: x86_64-macos.13-none }
           - { zig_target: x86_64-windows-gnu }
     env:
-      # 2023-05-02
-      ZIG_DIST_VERSION: 0.11.0-dev.2939+289234744
+      # 2023-05-06
+      ZIG_DIST_VERSION: 0.11.0-dev.2991+9f3f9fb40
       # for zig-cc wrapper scripts (see below):
       ZIG_CPPFLAGS: -DUPX_DOCTEST_CONFIG_MULTITHREADING
       ZIG_FLAGS: ${{ matrix.zig_flags }}
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 724de2ce..5511318a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -232,9 +232,8 @@ if(MSVC_FRONTEND)
     target_compile_options(${t} PRIVATE -W3 ${warn_WX})
 else()
     target_compile_definitions(${t} PRIVATE HAVE_UNISTD_H=1)
-    # clang-15: -Wno-strict-prototypes is needed to silence the new -Wdeprecated-non-prototype warning
-    target_compile_options(${t} PRIVATE -Wall -Wno-strict-prototypes ${warn_Werror})
-    ##target_compile_options(${t} PRIVATE ${warn_Wall} -Wno-cast-align -Wno-cast-qual -Wno-strict-prototypes ${warn_Werror})
+    target_compile_options(${t} PRIVATE -Wall ${warn_Werror})
+    ##target_compile_options(${t} PRIVATE ${warn_Wall} -Wno-cast-align -Wno-cast-qual ${warn_Werror})
 endif()
 
 if(NOT UPX_CONFIG_DISABLE_ZSTD)
diff --git a/src/bele.h b/src/bele.h
index 4c7f7aaf..0daf72b5 100644
--- a/src/bele.h
+++ b/src/bele.h
@@ -26,8 +26,6 @@
  */
 
 #pragma once
-#ifndef UPX_BELE_H__
-#define UPX_BELE_H__ 1
 
 // BE - Big Endian
 // LE - Little Endian
@@ -753,6 +751,4 @@ inline const N_BELE_RTP::AbstractPolicy *getRTP(const LEPolicy * /*dummy*/) {
 }
 } // namespace N_BELE_CTP
 
-#endif /* already included */
-
 /* vim:set ts=4 sw=4 et: */
diff --git a/src/bele_policy.h b/src/bele_policy.h
index f1e8cf26..cfc11598 100644
--- a/src/bele_policy.h
+++ b/src/bele_policy.h
@@ -25,9 +25,7 @@
    <markus@oberhumer.com>               <ezerotven+github@gmail.com>
  */
 
-#ifndef UPX_BELE_H__
-#error "this is an internal include file"
-#endif
+// this is an internal include file private to bele.h
 
 /*************************************************************************
 //
diff --git a/src/conf.h b/src/conf.h
index 711a3659..bdeb82f5 100644
--- a/src/conf.h
+++ b/src/conf.h
@@ -144,10 +144,10 @@ typedef unsigned char   byte;
 #define upx_byte        byte
 #define upx_bytep       byte *
 typedef unsigned char   uchar;
-// use "charptr" when dealing with pointer arithmetics
+// convention: use "charptr" when dealing with abstract pointer arithmetics
 #define charptr         upx_charptr_unit_type *
 // upx_charptr_unit_type is some opaque type with sizeof(type) == 1
-struct alignas(1) upx_charptr_unit_type { char dummy; };
+struct alignas(1) upx_charptr_unit_type { char hidden__; };
 ACC_COMPILE_TIME_ASSERT_HEADER(sizeof(upx_charptr_unit_type) == 1)
 
 // using the system off_t was a bad idea even back in 199x...
diff --git a/src/file.h b/src/file.h
index ecf8627f..19203001 100644
--- a/src/file.h
+++ b/src/file.h
@@ -26,8 +26,6 @@
  */
 
 #pragma once
-#ifndef UPX_FILE_H__
-#define UPX_FILE_H__ 1
 
 /*************************************************************************
 //
@@ -129,6 +127,4 @@ protected:
     upx_off_t bytes_written = 0;
 };
 
-#endif
-
 /* vim:set ts=4 sw=4 et: */
diff --git a/src/main.cpp b/src/main.cpp
index 0a749df1..dcc18563 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -87,8 +87,9 @@ static void do_exit(void) {
 static bool set_eec(int ec, int *eec) {
     if (ec == EXIT_FATAL) {
         *eec = EXIT_ERROR;
-        return 1;
-    } else if (ec < 0 || ec == EXIT_ERROR) {
+        return true;
+    }
+    if (ec < 0 || ec == EXIT_ERROR) {
         *eec = EXIT_ERROR;
     } else if (ec == EXIT_WARN) {
         if (!opt->ignorewarn)
@@ -99,7 +100,7 @@ static bool set_eec(int ec, int *eec) {
     } else {
         assert(0);
     }
-    return 0;
+    return false;
 }
 
 bool main_set_exit_code(int ec) { return set_eec(ec, &exit_code); }
@@ -632,22 +633,22 @@ static int do_option(int optc, const char *arg) {
     // CPU
     case 560:
         if (mfx_optarg && strcmp(mfx_optarg, "8086") == 0)
-            opt->cpu = opt->CPU_8086;
+            opt->cpu_x86 = opt->CPU_8086;
         else if (mfx_optarg && strcmp(mfx_optarg, "386") == 0)
-            opt->cpu = opt->CPU_386;
+            opt->cpu_x86 = opt->CPU_386;
         else if (mfx_optarg && strcmp(mfx_optarg, "486") == 0)
-            opt->cpu = opt->CPU_486;
+            opt->cpu_x86 = opt->CPU_486;
         else
             e_optarg(arg);
         break;
     case 561:
-        opt->cpu = opt->CPU_8086;
+        opt->cpu_x86 = opt->CPU_8086;
         break;
     case 563:
-        opt->cpu = opt->CPU_386;
+        opt->cpu_x86 = opt->CPU_386;
         break;
     case 564:
-        opt->cpu = opt->CPU_486;
+        opt->cpu_x86 = opt->CPU_486;
         break;
     //
     case 600:
diff --git a/src/options.h b/src/options.h
index aae90bea..1db78476 100644
--- a/src/options.h
+++ b/src/options.h
@@ -26,11 +26,9 @@
  */
 
 #pragma once
-#ifndef UPX_OPTIONS_H__
-#define UPX_OPTIONS_H__ 1
 
 struct Options;
-extern Options *opt;
+extern Options *opt;      // global options, see class PackMaster for per-file local options
 #define options_t Options // old name
 
 #if WITH_THREADS
@@ -38,10 +36,10 @@ extern std::mutex opt_lock_mutex;
 #endif
 
 /*************************************************************************
-// globals
+// command line options
 **************************************************************************/
 
-// options - command
+// main command
 enum {
     CMD_NONE,
     CMD_COMPRESS,
@@ -105,20 +103,20 @@ struct Options final {
     int overlay;
 
     // CRP - Compression Runtime Parameters (undocumented and subject to change)
-    // see struct XXX_compress_config_t
-    struct crp_t {
+    struct {
         lzma_compress_config_t crp_lzma;
         ucl_compress_config_t crp_ucl;
         zlib_compress_config_t crp_zlib;
+        zstd_compress_config_t crp_zstd;
         void reset() {
             crp_lzma.reset();
             crp_ucl.reset();
             crp_zlib.reset();
+            crp_zstd.reset();
         }
-    };
-    crp_t crp;
+    } crp;
 
-    // CPU
+    // CPU options for i086/i386
     enum {
         CPU_DEFAULT = 0,
         CPU_8086 = 1,
@@ -126,7 +124,7 @@ struct Options final {
         CPU_386 = 3,
         CPU_486 = 4,
     };
-    int cpu;
+    int cpu_x86;
 
     // options for various executable formats
     struct {
@@ -172,6 +170,4 @@ struct Options final {
     void reset();
 };
 
-#endif /* already included */
-
 /* vim:set ts=4 sw=4 et: */
diff --git a/src/p_com.cpp b/src/p_com.cpp
index 232d0f7e..fbb558d5 100644
--- a/src/p_com.cpp
+++ b/src/p_com.cpp
@@ -88,7 +88,7 @@ void PackCom::addFilter16(int filter_id) {
         // clang-format off
         addLoader("CALLTR16",
                   filter_id < 4 ? "CT16SUB0" : "",
-                  filter_id < 4 ? "" : (opt->cpu == opt->CPU_8086 ? "CT16I086" : "CT16I286,CT16SUB0"),
+                  filter_id < 4 ? "" : (opt->cpu_x86 == opt->CPU_8086 ? "CT16I086" : "CT16I286,CT16SUB0"),
                   "CALLTRI2",
                   getFormat() == UPX_F_DOS_COM ? "CORETURN" : "");
         // clang-format on
@@ -98,7 +98,7 @@ void PackCom::addFilter16(int filter_id) {
                  "CALLTRI5",
                  getFormat() == UPX_F_DOS_COM ? "CT16JEND" : "CT16JUL2",
                  filter_id < 4 ? "CT16SUB1" : "",
-                 filter_id < 4 ? "" : (opt->cpu == opt->CPU_8086 ? "CT16I087" : "CT16I287,CT16SUB1"),
+                 filter_id < 4 ? "" : (opt->cpu_x86 == opt->CPU_8086 ? "CT16I087" : "CT16I287,CT16SUB1"),
                  "CALLTRI6");
         // clang-format on
     }
diff --git a/src/p_exe.cpp b/src/p_exe.cpp
index bf15a16e..5b58f7b0 100644
--- a/src/p_exe.cpp
+++ b/src/p_exe.cpp
@@ -186,18 +186,18 @@ void PackExe::buildLoader(const Filter *) {
     if (ph.method == M_NRV2B_8)
         addLoader("NRV2B16S", // decompressor
                   ph.u_len > DI_LIMIT ? "N2B64K01" : "", "NRV2BEX1",
-                  opt->cpu == opt->CPU_8086 ? "N2BX8601" : "N2B28601", "NRV2BEX2",
-                  opt->cpu == opt->CPU_8086 ? "N2BX8602" : "N2B28602", "NRV2BEX3",
+                  opt->cpu_x86 == opt->CPU_8086 ? "N2BX8601" : "N2B28601", "NRV2BEX2",
+                  opt->cpu_x86 == opt->CPU_8086 ? "N2BX8602" : "N2B28602", "NRV2BEX3",
                   ph.c_len > 0xffff ? "N2B64K02" : "", "NRV2BEX9");
     else if (ph.method == M_NRV2D_8)
         addLoader("NRV2D16S", ph.u_len > DI_LIMIT ? "N2D64K01" : "", "NRV2DEX1",
-                  opt->cpu == opt->CPU_8086 ? "N2DX8601" : "N2D28601", "NRV2DEX2",
-                  opt->cpu == opt->CPU_8086 ? "N2DX8602" : "N2D28602", "NRV2DEX3",
+                  opt->cpu_x86 == opt->CPU_8086 ? "N2DX8601" : "N2D28601", "NRV2DEX2",
+                  opt->cpu_x86 == opt->CPU_8086 ? "N2DX8602" : "N2D28602", "NRV2DEX3",
                   ph.c_len > 0xffff ? "N2D64K02" : "", "NRV2DEX9");
     else if (ph.method == M_NRV2E_8)
         addLoader("NRV2E16S", ph.u_len > DI_LIMIT ? "N2E64K01" : "", "NRV2EEX1",
-                  opt->cpu == opt->CPU_8086 ? "N2EX8601" : "N2E28601", "NRV2EEX2",
-                  opt->cpu == opt->CPU_8086 ? "N2EX8602" : "N2E28602", "NRV2EEX3",
+                  opt->cpu_x86 == opt->CPU_8086 ? "N2EX8601" : "N2E28601", "NRV2EEX2",
+                  opt->cpu_x86 == opt->CPU_8086 ? "N2EX8602" : "N2E28602", "NRV2EEX3",
                   ph.c_len > 0xffff ? "N2E64K02" : "", "NRV2EEX9");
     else if M_IS_LZMA (ph.method)
         return;
diff --git a/src/p_sys.cpp b/src/p_sys.cpp
index 2ff40c68..46246cb7 100644
--- a/src/p_sys.cpp
+++ b/src/p_sys.cpp
@@ -64,7 +64,7 @@ void PackSys::buildLoader(const Filter *ft) {
     initLoader(stub_i086_dos16_sys, sizeof(stub_i086_dos16_sys));
     // clang-format off
     addLoader("SYSMAIN1",
-              opt->cpu == opt->CPU_8086 ? "SYSI0861" : "SYSI2861",
+              opt->cpu_x86 == opt->CPU_8086 ? "SYSI0861" : "SYSI2861",
               "SYSMAIN2",
               ph.first_offset_found == 1 ? "SYSSBBBP" : "",
               ft->id ? "SYSCALLT" : "",
@@ -78,7 +78,7 @@ void PackSys::buildLoader(const Filter *ft) {
     }
     // clang-format off
     addLoader("SYSMAIN5",
-              opt->cpu == opt->CPU_8086 ? "SYSI0862" : "SYSI2862",
+              opt->cpu_x86 == opt->CPU_8086 ? "SYSI0862" : "SYSI2862",
               "SYSJUMP1");
     // clang-format on
 }
diff --git a/src/p_wince_arm.cpp b/src/p_wince_arm.cpp
index 4626a739..fb7f7a7b 100644
--- a/src/p_wince_arm.cpp
+++ b/src/p_wince_arm.cpp
@@ -118,7 +118,8 @@ bool PackWinCeArm::canPack() {
     if (ih.cpu != IMAGE_FILE_MACHINE_ARM && ih.cpu != IMAGE_FILE_MACHINE_THUMB)
         return false;
     use_thumb_stub |= ih.cpu == IMAGE_FILE_MACHINE_THUMB || (ih.entry & 1) == 1;
-    use_thumb_stub |= (opt->cpu == opt->CPU_8086); // FIXME
+    // FIXME later: don't misuse opt->cpu_x86, need an extra option for thumb
+    use_thumb_stub |= (opt->cpu_x86 == opt->CPU_8086);
     return true;
 }
 
diff --git a/src/packer_f.cpp b/src/packer_f.cpp
index f2b20d00..607834e6 100644
--- a/src/packer_f.cpp
+++ b/src/packer_f.cpp
@@ -90,7 +90,7 @@ void Packer::addFilter32(int filter_id) {
                       "CALLTR13");
     }
     if (0x80 == (filter_id & 0xF0)) {
-        bool const x386 = (opt->cpu <= opt->CPU_386);
+        bool const x386 = (opt->cpu_x86 <= opt->CPU_386);
         const unsigned n_mru = ph.n_mru ? 1 + ph.n_mru : 0;
         bool const mrupwr2 = (0 != n_mru) && 0 == ((n_mru - 1) & n_mru);
         const unsigned f_call = f80_call(filter_id);
diff --git a/src/pefile.h b/src/pefile.h
index 5a7e81fc..e932363c 100644
--- a/src/pefile.h
+++ b/src/pefile.h
@@ -334,7 +334,7 @@ protected:
         IMAGE_SUBSYSTEM_WINDOWS_BOOT_APPLICATION = 16,
     };
 
-    // predefined resource types
+    // predefined Resource Types
     enum {
         RT_CURSOR = 1,
         RT_BITMAP,
diff --git a/src/util/membuffer.cpp b/src/util/membuffer.cpp
index 1da7ca5e..6da2a9dd 100644
--- a/src/util/membuffer.cpp
+++ b/src/util/membuffer.cpp
@@ -287,6 +287,37 @@ TEST_CASE("MemBuffer") {
     }
 }
 
+TEST_CASE("MemBuffer global overloads") {
+    MemBuffer mb(1);
+    MemBuffer mb4(4);
+    mb.clear();
+    mb4.clear();
+    CHECK(memcmp(mb, "\x00", 1) == 0);
+    CHECK_THROWS(memcmp(mb, "\x00\x00", 2));
+    CHECK_THROWS(memcmp("\x00\x00", mb, 2));
+    CHECK_THROWS(memcmp(mb, mb4, 2));
+    CHECK_THROWS(memcmp(mb4, mb, 2));
+    CHECK_NOTHROW(memset(mb, 255, 1));
+    CHECK_THROWS(memset(mb, 254, 2));
+    CHECK(mb[0] == 255);
+    CHECK_THROWS(get_be16(mb));
+    CHECK_THROWS(get_be32(mb));
+    CHECK_THROWS(get_be64(mb));
+    CHECK_THROWS(get_le16(mb));
+    CHECK_THROWS(get_le32(mb));
+    CHECK_THROWS(get_le64(mb));
+    CHECK_NOTHROW(get_be16(mb4));
+    CHECK_NOTHROW(get_be32(mb4));
+    CHECK_THROWS(get_be64(mb4));
+    CHECK_NOTHROW(get_le16(mb4));
+    CHECK_NOTHROW(get_le32(mb4));
+    CHECK_THROWS(get_le64(mb4));
+    CHECK_NOTHROW(set_be32(mb4, 0));
+    CHECK_THROWS(set_be64(mb4, 0));
+    CHECK_NOTHROW(set_le32(mb4, 0));
+    CHECK_THROWS(set_le64(mb4, 0));
+}
+
 TEST_CASE("MemBuffer unused") {
     MemBuffer mb;
     CHECK(mb.raw_ptr() == nullptr);
diff --git a/src/util/membuffer.h b/src/util/membuffer.h
index 895b9bba..d7411adf 100644
--- a/src/util/membuffer.h
+++ b/src/util/membuffer.h
@@ -27,19 +27,20 @@
 
 #pragma once
 
-/*************************************************************************
 // A MemBuffer allocates memory on the heap, and automatically
 // gets destructed when leaving scope or on exceptions.
+
+/*************************************************************************
+// provides some base functionality for treating a MemBuffer as a pointer
 **************************************************************************/
 
-// provides some base functionality for treating a MemBuffer as a pointer
 template <class T>
 class MemBufferBase {
 public:
     typedef T element_type;
     typedef typename std::add_lvalue_reference<T>::type reference;
     typedef typename std::add_pointer<T>::type pointer;
-    typedef unsigned size_type;
+    typedef unsigned size_type; // limited by UPX_RSIZE_MAX
 
 protected:
     pointer ptr;
@@ -79,8 +80,61 @@ public: // raw access
         }
         return ptr;
     }
+
+private:
+    // disable taking the address => force passing by reference
+    // [I'm not too sure about this design decision, but we can always allow it if needed]
+    MemBufferBase<T> *operator&() const DELETED_FUNCTION;
 };
 
+/*************************************************************************
+// MemBufferBase global overloads
+**************************************************************************/
+
+// global operators
+#if ALLOW_INT_PLUS_MEMBUFFER
+// rewrite "n + membuffer" to "membuffer + n" so that this will get checked above
+template <class T, class U>
+inline typename std::enable_if<std::is_integral<U>::value, typename MemBufferBase<T>::pointer>::type
+operator+(U n, const MemBufferBase<T> &mbb) {
+    return mbb + n;
+}
+#else
+// not allowed
+template <class T, class U>
+inline typename std::enable_if<std::is_integral<U>::value, typename MemBufferBase<T>::pointer>::type
+operator+(U n, const MemBufferBase<T> &mbb) DELETED_FUNCTION;
+#endif
+
+// raw_bytes overload
+template <class T>
+inline typename MemBufferBase<T>::pointer raw_bytes(const MemBufferBase<T> &mbb,
+                                                    size_t size_in_bytes) {
+    return mbb.raw_bytes(size_in_bytes);
+}
+template <class T>
+inline typename MemBufferBase<T>::pointer raw_index_bytes(const MemBufferBase<T> &mbb, size_t index,
+                                                          size_t size_in_bytes) {
+    typedef typename MemBufferBase<T>::element_type element_type;
+    return mbb.raw_bytes(mem_size(sizeof(element_type), index, size_in_bytes)) + index;
+}
+
+#if 1
+// some more global overloads using a checked raw_bytes() call
+#define XSPAN_REQUIRES_CONVERTIBLE_ANY_DIRECTION(A, B, RType)                                      \
+    typename std::enable_if<std::is_same<A, B>::value, RType>::type
+#define XSPAN_FWD_C_IS_MEMBUFFER 1
+#define C MemBufferBase
+#include "xspan_fwd.h"
+#undef C
+#undef XSPAN_FWD_C_IS_MEMBUFFER
+#undef XSPAN_REQUIRES_CONVERTIBLE_ANY_DIRECTION
+#endif
+
+/*************************************************************************
+//
+**************************************************************************/
+
 class MemBuffer final : public MemBufferBase<byte> {
 public:
     inline MemBuffer() noexcept : MemBufferBase<byte>() {}
@@ -147,37 +201,6 @@ private:
 #endif
     // disable dynamic allocation
     ACC_CXX_DISABLE_NEW_DELETE
-
-    // disable taking the address => force passing by reference
-    // [I'm not too sure about this design decision, but we can always allow it if needed]
-    MemBuffer *operator&() const DELETED_FUNCTION;
 };
 
-// raw_bytes overload
-template <class T>
-inline typename MemBufferBase<T>::pointer raw_bytes(const MemBufferBase<T> &mbb,
-                                                    size_t size_in_bytes) {
-    return mbb.raw_bytes(size_in_bytes);
-}
-template <class T>
-inline typename MemBufferBase<T>::pointer raw_index_bytes(const MemBufferBase<T> &mbb, size_t index,
-                                                          size_t size_in_bytes) {
-    typedef typename MemBufferBase<T>::element_type element_type;
-    return mbb.raw_bytes(mem_size(sizeof(element_type), index, size_in_bytes)) + index;
-}
-
-// global operators
-#if ALLOW_INT_PLUS_MEMBUFFER
-// rewrite "n + membuffer" to "membuffer + n" so that this will get checked above
-template <class T, class U>
-inline typename std::enable_if<std::is_integral<U>::value, typename MemBufferBase<T>::pointer>::type
-operator+(U n, const MemBufferBase<T> &mbb) {
-    return mbb + n;
-}
-#else
-template <class T, class U>
-inline typename std::enable_if<std::is_integral<U>::value, typename MemBufferBase<T>::pointer>::type
-operator+(U n, const MemBufferBase<T> &mbb) DELETED_FUNCTION;
-#endif
-
 /* vim:set ts=4 sw=4 et: */
diff --git a/src/util/xspan_fwd.h b/src/util/xspan_fwd.h
index b28f4d06..564907b0 100644
--- a/src/util/xspan_fwd.h
+++ b/src/util/xspan_fwd.h
@@ -31,21 +31,23 @@
     template <class T, class U>                                                                    \
     inline XSPAN_REQUIRES_CONVERTIBLE_ANY_DIRECTION(T, U, RType)
 
+#ifndef XSPAN_FWD_C_IS_MEMBUFFER
 template <class T, class U>
 inline typename std::enable_if<std::is_integral<U>::value, void *>::type operator+(U, const C<T> &)
     DELETED_FUNCTION;
+#endif // XSPAN_FWD_C_IS_MEMBUFFER
 
 /*************************************************************************
 // overloads for standard functions
 **************************************************************************/
 
 template <class T>
-inline void *memchr(const C<T> &a, int c, size_t n) {
-    return memchr(a.raw_bytes(n), c, n);
+inline void *memchr(const C<T> &a, int v, size_t n) {
+    return memchr(a.raw_bytes(n), v, n);
 }
 template <class T>
-inline const void *memchr(const C<const T> &a, int c, size_t n) {
-    return memchr(a.raw_bytes(n), c, n);
+inline const void *memchr(const C<const T> &a, int v, size_t n) {
+    return memchr(a.raw_bytes(n), v, n);
 }
 
 template <class T>
@@ -115,8 +117,8 @@ XSPAN_FWD_TU(void *) memmove(const C<T> &a, const E<U> &b, size_t n) {
 #endif
 
 template <class T>
-inline void *memset(const C<T> &a, int c, size_t n) {
-    return memset(a.raw_bytes(n), c, n);
+inline void *memset(const C<T> &a, int v, size_t n) {
+    return memset(a.raw_bytes(n), v, n);
 }
 
 /*************************************************************************
@@ -255,6 +257,7 @@ void set_le64(const C<T> &a, upx_uint64_t v) {
     return set_le64(a.raw_bytes(8), v);
 }
 
+#ifndef XSPAN_FWD_C_IS_MEMBUFFER
 template <class T>
 inline C<T> operator+(const C<T> &a, const BE16 &v) {
     return a + unsigned(v);
@@ -288,6 +291,7 @@ template <class T>
 inline C<T> operator-(const C<T> &a, const LE32 &v) {
     return a - unsigned(v);
 }
+#endif // XSPAN_FWD_C_IS_MEMBUFFER
 
 template <class T>
 typename std::enable_if<sizeof(T) == 1, upx_rsize_t>::type upx_safe_strlen(const C<T> &a) {