diff --git a/CMakeLists.txt b/CMakeLists.txt
index d4b76ac8..afa5673d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -36,36 +36,36 @@ endif()
 
 include(SetPaths.cmake)
 
-include(CheckCXXCompilerFlag)
+include(CheckCCompilerFlag)
 include(CheckFunctionExists)
 
 if(NOT MSVC) # Use default warnings if MSVC otherwise inundated
-    check_cxx_compiler_flag("-Wall" CXX_COMPILER_FLAG_WALL)
-    if(CXX_COMPILER_FLAG_WALL)
+    check_c_compiler_flag("-Wall" C_COMPILER_FLAG_WALL)
+    if(C_COMPILER_FLAG_WALL)
         add_compile_options("-Wall")
     endif()
 
-    check_cxx_compiler_flag("-Wextra" CXX_COMPILER_FLAG_WEXTRA)
-    if(CXX_COMPILER_FLAG_WEXTRA)
+    check_c_compiler_flag("-Wextra" C_COMPILER_FLAG_WEXTRA)
+    if(C_COMPILER_FLAG_WEXTRA)
         add_compile_options("-Wextra")
     endif()
 
-    check_cxx_compiler_flag("-Wpedantic" CXX_COMPILER_FLAG_WPEDANTIC)
-    if(CXX_COMPILER_FLAG_WPEDANTIC)
+    check_c_compiler_flag("-Wpedantic" C_COMPILER_FLAG_WPEDANTIC)
+    if(C_COMPILER_FLAG_WPEDANTIC)
         add_compile_options("-Wpedantic")
     endif()
 endif()
 
 if(ZINT_DEBUG)
-    check_cxx_compiler_flag("-g" CXX_COMPILER_FLAG_G)
-    if(CXX_COMPILER_FLAG_G)
+    check_c_compiler_flag("-g" C_COMPILER_FLAG_G)
+    if(C_COMPILER_FLAG_G)
         add_compile_options("-g")
     endif()
 endif()
 
 if(ZINT_NOOPT)
-    check_cxx_compiler_flag("-O0" CXX_COMPILER_FLAG_O0)
-    if(CXX_COMPILER_FLAG_O0)
+    check_c_compiler_flag("-O0" C_COMPILER_FLAG_O0)
+    if(C_COMPILER_FLAG_O0)
         add_compile_options("-O0")
     endif()
 endif()
@@ -82,19 +82,19 @@ if(ZINT_SANITIZE)
         set(SANITIZERS address undefined)
         foreach(sanitizer IN ITEMS ${SANITIZERS})
             set(CMAKE_REQUIRED_LIBRARIES -fsanitize=${sanitizer})
-            check_cxx_compiler_flag(-fsanitize=${sanitizer} CXX_COMPILER_FLAG_FSANITIZE_${sanitizer})
-            if(CXX_COMPILER_FLAG_FSANITIZE_${sanitizer})
+            check_c_compiler_flag(-fsanitize=${sanitizer} C_COMPILER_FLAG_FSANITIZE_${sanitizer})
+            if(C_COMPILER_FLAG_FSANITIZE_${sanitizer})
                 add_compile_options(-fsanitize=${sanitizer})
                 link_libraries(-fsanitize=${sanitizer})
             endif()
             unset(CMAKE_REQUIRED_LIBRARIES)
         endforeach()
 
-        if(NOT ZINT_DEBUG AND CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+        if(NOT ZINT_DEBUG AND CMAKE_C_COMPILER_ID MATCHES "GNU")
             # Gives warning on MainWindow::setupUI() and retries (& takes forever) if var-tracking-assignments enabled
             add_compile_options(-fno-var-tracking-assignments)
         endif()
-        if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+        if(CMAKE_C_COMPILER_ID MATCHES "Clang")
             # Recent clangs added deprecation warnings for `sprintf()` that are only triggered on sanitize - suppress
             add_compile_options(-Wno-deprecated-declarations)
         endif()
@@ -107,14 +107,14 @@ endif()
 
 if(ZINT_COVERAGE)
     set(CMAKE_REQUIRED_LIBRARIES -fprofile-arcs)
-    check_cxx_compiler_flag(--coverage CXX_COMPILER_FLAG_COVERAGE)
+    check_c_compiler_flag(--coverage C_COMPILER_FLAG_COVERAGE)
     unset(CMAKE_REQUIRED_LIBRARIES)
-    if(CXX_COMPILER_FLAG_COVERAGE)
+    if(C_COMPILER_FLAG_COVERAGE)
         add_compile_options(--coverage)
         link_libraries(-fprofile-arcs)
 
-        check_cxx_compiler_flag(-O0 CXX_COMPILER_FLAG_O0)
-        if(CXX_COMPILER_FLAG_O0)
+        check_c_compiler_flag(-O0 C_COMPILER_FLAG_O0)
+        if(C_COMPILER_FLAG_O0)
             add_compile_options(-O0)
         endif()
     endif()
diff --git a/backend/bmp.h b/backend/bmp.h
index 3cb00f11..6de4c911 100644
--- a/backend/bmp.h
+++ b/backend/bmp.h
@@ -1,7 +1,7 @@
 /*  bmp.h - header structure for Windows bitmap files */
 /*
     libzint - the open source barcode library
-    Copyright (C) 2009-2022 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2009-2024 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -37,14 +37,16 @@
 extern "C" {
 #endif
 
-#pragma pack (1)
+#ifdef _MSC_VER
+#pragma pack(1)
+#endif
 
     typedef struct bitmap_file_header {
         uint16_t header_field;
         uint32_t file_size;
         uint32_t reserved;
         uint32_t data_offset;
-    } bitmap_file_header_t;
+    } OUT_PACK bitmap_file_header_t;
 
     typedef struct bitmap_info_header {
         uint32_t header_size;
@@ -58,16 +60,18 @@ extern "C" {
         int32_t vert_res;
         uint32_t colours;
         uint32_t important_colours;
-    } bitmap_info_header_t;
+    } OUT_PACK bitmap_info_header_t;
 
     typedef struct color_ref {
         uint8_t blue;
         uint8_t green;
         uint8_t red;
         uint8_t reserved;
-    } color_ref_t;
+    } OUT_PACK color_ref_t;
 
-#pragma pack ()
+#ifdef _MSC_VER
+#pragma pack()
+#endif
 
 #ifdef __cplusplus
 }
diff --git a/backend/code.c b/backend/code.c
index 635871f7..dd5772ae 100644
--- a/backend/code.c
+++ b/backend/code.c
@@ -631,19 +631,19 @@ static void channel_generate_precalc(int channels, long value, int mod, int last
 #include "channel_precalcs.h"
 #endif
 
-static long channel_copy_precalc(channel_precalc precalc, int B[8], int S[8], int bmax[7], int smax[7]) {
+static long channel_copy_precalc(channel_precalc *const precalc, int B[8], int S[8], int bmax[7], int smax[7]) {
     int i;
 
     for (i = 0; i < 7; i++) {
-        B[i] = precalc.B[i];
-        S[i] = precalc.S[i];
-        bmax[i] = precalc.bmax[i];
-        smax[i] = precalc.smax[i];
+        B[i] = precalc->B[i];
+        S[i] = precalc->S[i];
+        bmax[i] = precalc->bmax[i];
+        smax[i] = precalc->smax[i];
     }
-    B[7] = precalc.B[7];
-    S[7] = precalc.S[7];
+    B[7] = precalc->B[7];
+    S[7] = precalc->S[7];
 
-    return precalc.value;
+    return precalc->value;
 }
 
 /* CHNCHR is adapted from ANSI/AIM BC12-1998 Annex D Figure D5 and is Copyright (c) AIM 1997 */
@@ -676,14 +676,14 @@ static void CHNCHR(int channels, long target_value, int B[8], int S[8]) {
     int bmax[7], smax[7];
     long value = 0;
 
-    channel_copy_precalc(initial_precalcs[channels - 3], B, S, bmax, smax);
+    channel_copy_precalc(&initial_precalcs[channels - 3], B, S, bmax, smax);
 
 #ifndef CHANNEL_GENERATE_PRECALCS
     if (channels == 7 && target_value >= channel_precalcs7[0].value) {
-        value = channel_copy_precalc(channel_precalcs7[(target_value / channel_precalcs7[0].value) - 1], B, S, bmax,
+        value = channel_copy_precalc(&channel_precalcs7[(target_value / channel_precalcs7[0].value) - 1], B, S, bmax,
                                     smax);
     } else if (channels == 8 && target_value >= channel_precalcs8[0].value) {
-        value = channel_copy_precalc(channel_precalcs8[(target_value / channel_precalcs8[0].value) - 1], B, S, bmax,
+        value = channel_copy_precalc(&channel_precalcs8[(target_value / channel_precalcs8[0].value) - 1], B, S, bmax,
                                     smax);
     }
 #endif
diff --git a/backend/emf.h b/backend/emf.h
index 1f5de457..599cdb93 100644
--- a/backend/emf.h
+++ b/backend/emf.h
@@ -1,7 +1,7 @@
 /*  emf.h - header structure for Microsoft EMF */
 /*
     libzint - the open source barcode library
-    Copyright (C) 2016-2022 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2016-2024 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -37,43 +37,45 @@
 extern "C" {
 #endif
 
+#ifdef _MSC_VER
 #pragma pack(1)
+#endif
 
     typedef struct rect_l {
         int32_t left;
         int32_t top;
         int32_t right;
         int32_t bottom;
-    } rect_l_t;
+    } OUT_PACK rect_l_t;
 
     typedef struct size_l {
         uint32_t cx;
         uint32_t cy;
-    } size_l_t;
+    } OUT_PACK size_l_t;
 
     typedef struct point_l {
         int32_t x;
         int32_t y;
-    } point_l_t;
+    } OUT_PACK point_l_t;
 
     typedef struct color_ref {
         uint8_t red;
         uint8_t green;
         uint8_t blue;
         uint8_t reserved;
-    } color_ref_t;
+    } OUT_PACK color_ref_t;
 
     typedef struct log_brush_ex {
         uint32_t brush_style;
         color_ref_t color;
         uint32_t brush_hatch;
-    } log_brush_ex_t;
+    } OUT_PACK log_brush_ex_t;
 
     typedef struct log_pen {
         uint32_t pen_style;
         point_l_t width;
         color_ref_t color_ref;
-    } log_pen_t;
+    } OUT_PACK log_pen_t;
 
     typedef struct log_font {
         int32_t height;
@@ -90,7 +92,7 @@ extern "C" {
         uint8_t quality;
         uint8_t pitch_and_family;
         unsigned char facename[64];
-    } log_font_t;
+    } OUT_PACK log_font_t;
 
     typedef struct emr_text {
         point_l_t reference;
@@ -99,7 +101,7 @@ extern "C" {
         uint32_t options;
         rect_l_t rectangle;
         uint32_t off_dx;
-    } emr_text_t;
+    } OUT_PACK emr_text_t;
 
     typedef struct emf_header {
         rect_l_t bounds;
@@ -121,19 +123,19 @@ extern "C" {
         uint32_t b_open_gl;
         /* HeaderExtension2 Object */
         size_l_t micrometers;
-    } emf_header_t;
+    } OUT_PACK emf_header_t;
 
     typedef struct emr_header {
         uint32_t type;
         uint32_t size;
         emf_header_t emf_header;
-    } emr_header_t;
+    } OUT_PACK emr_header_t;
 
     typedef struct emr_mapmode {
         uint32_t type;
         uint32_t size;
         uint32_t mapmode;
-    } emr_mapmode_t;
+    } OUT_PACK emr_mapmode_t;
 
     typedef struct emr_setworldtransform {
         uint32_t type;
@@ -144,39 +146,39 @@ extern "C" {
         float m22;
         float dx;
         float dy;
-    } emr_setworldtransform_t;
+    } OUT_PACK emr_setworldtransform_t;
 
     typedef struct emr_createbrushindirect {
         uint32_t type;
         uint32_t size;
         uint32_t ih_brush;
         log_brush_ex_t log_brush;
-    } emr_createbrushindirect_t;
+    } OUT_PACK emr_createbrushindirect_t;
 
     typedef struct emr_createpen {
         uint32_t type;
         uint32_t size;
         uint32_t ih_pen;
         log_pen_t log_pen;
-    } emr_createpen_t;
+    } OUT_PACK emr_createpen_t;
 
     typedef struct emr_selectobject {
         uint32_t type;
         uint32_t size;
         uint32_t ih_object;
-    } emr_selectobject_t;
+    } OUT_PACK emr_selectobject_t;
 
     typedef struct emr_rectangle {
         uint32_t type;
         uint32_t size;
         rect_l_t box;
-    } emr_rectangle_t;
+    } OUT_PACK emr_rectangle_t;
 
     typedef struct emr_ellipse {
         uint32_t type;
         uint32_t size;
         rect_l_t box;
-    } emr_ellipse_t;
+    } OUT_PACK emr_ellipse_t;
 
     typedef struct emr_polygon {
         uint32_t type;
@@ -189,26 +191,26 @@ extern "C" {
         point_l_t a_points_d;
         point_l_t a_points_e;
         point_l_t a_points_f;
-    } emr_polygon_t;
+    } OUT_PACK emr_polygon_t;
 
     typedef struct emr_extcreatefontindirectw {
         uint32_t type;
         uint32_t size;
         uint32_t ih_fonts;
         log_font_t elw;
-    } emr_extcreatefontindirectw_t;
+    } OUT_PACK emr_extcreatefontindirectw_t;
 
     typedef struct emr_settextalign {
         uint32_t type;
         uint32_t size;
         uint32_t text_alignment_mode;
-    } emr_settextalign_t;
+    } OUT_PACK emr_settextalign_t;
 
     typedef struct emr_settextcolor {
         uint32_t type;
         uint32_t size;
         color_ref_t color;
-    } emr_settextcolor_t;
+    } OUT_PACK emr_settextcolor_t;
 
     typedef struct emr_exttextoutw {
         uint32_t type;
@@ -218,7 +220,7 @@ extern "C" {
         float ex_scale;
         float ey_scale;
         emr_text_t w_emr_text;
-    } emr_exttextoutw_t;
+    } OUT_PACK emr_exttextoutw_t;
 
     typedef struct emr_eof {
         uint32_t type;
@@ -226,16 +228,18 @@ extern "C" {
         uint32_t n_pal_entries;
         uint32_t off_pal_entries;
         uint32_t size_last;
-    } emr_eof_t;
+    } OUT_PACK emr_eof_t;
 
     typedef struct box {
         emr_rectangle_t top;
         emr_rectangle_t bottom;
         emr_rectangle_t left;
         emr_rectangle_t right;
-    } box_t;
+    } OUT_PACK box_t;
 
+#ifdef _MSC_VER
 #pragma pack()
+#endif
 
 #ifdef  __cplusplus
 }
diff --git a/backend/gif.c b/backend/gif.c
index 89b67522..7c5d8395 100644
--- a/backend/gif.c
+++ b/backend/gif.c
@@ -397,9 +397,9 @@ INTERNAL int gif_pixel_plot(struct zint_symbol *symbol, unsigned char *pixelbuf)
      */
     if (transparent_index != -1) {
         /* Extension Introducer = '!' */
-        outbuf[0] = '\x21';
+        outbuf[0] = '!';
         /* Graphic Control Label */
-        outbuf[1] = '\xf9';
+        outbuf[1] = 0xf9;
         /* Block Size */
         outbuf[2] = 4;
         /* Packet fields:
@@ -452,7 +452,7 @@ INTERNAL int gif_pixel_plot(struct zint_symbol *symbol, unsigned char *pixelbuf)
     free(State.pOut);
 
     /* GIF terminator */
-    fm_putc('\x3b', State.fmp);
+    fm_putc(';', State.fmp);
 
     if (fm_error(State.fmp)) {
         sprintf(symbol->errtxt, "615: Incomplete write to output (%d: %.30s)", State.fmp->err,
diff --git a/backend/output.h b/backend/output.h
index 6ff52fab..3dc18f59 100644
--- a/backend/output.h
+++ b/backend/output.h
@@ -113,6 +113,13 @@ INTERNAL FILE *out_win_fopen(const char *filename, const char *mode);
         bp[3] = (unsigned char) ((*p_u32 >> 24) & 0xFF); \
     } while (0)
 
+/* For more portability, use `#pragma pack()` pair for MSCV, per-type packed attribute otherwise */
+#ifdef _MSC_VER
+#  define OUT_PACK
+#else
+#  define OUT_PACK __attribute__((__packed__))
+#endif
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */
diff --git a/backend/pcx.h b/backend/pcx.h
index 3e141732..3debb3db 100644
--- a/backend/pcx.h
+++ b/backend/pcx.h
@@ -37,7 +37,9 @@
 extern "C" {
 #endif
 
-#pragma pack (1)
+#ifdef _MSC_VER
+#pragma pack(1)
+#endif
 
     typedef struct pcx_header {
         uint8_t manufacturer;
@@ -58,9 +60,11 @@ extern "C" {
         uint16_t horiz_screen_size;
         uint16_t vert_screen_size;
         uint8_t filler[54];
-    } pcx_header_t;
+    } OUT_PACK pcx_header_t;
 
-#pragma pack ()
+#ifdef _MSC_VER
+#pragma pack()
+#endif
 
 #ifdef __cplusplus
 }
diff --git a/backend/tif.h b/backend/tif.h
index 1709bc92..a9c8ea01 100644
--- a/backend/tif.h
+++ b/backend/tif.h
@@ -1,7 +1,7 @@
 /* tif.h - Aldus Tagged Image File Format */
 /*
     libzint - the open source barcode library
-    Copyright (C) 2016-2022 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2016-2024 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -37,28 +37,32 @@
 extern "C" {
 #endif
 
+#ifdef _MSC_VER
 #pragma pack(1)
+#endif
 
     typedef struct tiff_header {
         uint16_t byte_order;
         uint16_t identity;
         uint32_t offset;
-    } tiff_header_t;
+    } OUT_PACK tiff_header_t;
 
     typedef struct tiff_tag {
         uint16_t tag;
         uint16_t type;
         uint32_t count;
         uint32_t offset;
-    } tiff_tag_t;
+    } OUT_PACK tiff_tag_t;
 
     typedef struct tiff_color {
         uint16_t red;
         uint16_t green;
         uint16_t blue;
-    } tiff_color_t;
+    } OUT_PACK tiff_color_t;
 
+#ifdef _MSC_VER
 #pragma pack()
+#endif
 
 #ifdef  __cplusplus
 }