diff --git a/backend/aztec.c b/backend/aztec.c
index 278fb025..32ae8c6f 100644
--- a/backend/aztec.c
+++ b/backend/aztec.c
@@ -980,7 +980,8 @@ static int az_binary_string(const unsigned char source[], const int length, int
     const int entry_bp = bp;
 #endif
 
-    if (!az_state_list_init(list, length)) {
+    assert(length < USHRT_MAX);
+    if (!az_state_list_init(list, (unsigned short) length)) {
         return 0;
     }
     memset(list->states, 0, sizeof(struct az_state));
diff --git a/backend/common.c b/backend/common.c
index a4db539d..0b9b6740 100644
--- a/backend/common.c
+++ b/backend/common.c
@@ -960,7 +960,7 @@ INTERNAL void z_hrt_printf_nochk(struct zint_symbol *symbol, const char *fmt, ..
 
     va_start(ap, fmt);
 
-#ifdef ZINT_IS_C89
+#ifdef Z_NO_VSNPRINTF
     size = vsprintf((char *) symbol->text, fmt, ap);
 #else
     size = vsnprintf((char *) symbol->text, sizeof(symbol->text), fmt, ap);
diff --git a/backend/common.h b/backend/common.h
index 2573a5e6..d2da2e21 100644
--- a/backend/common.h
+++ b/backend/common.h
@@ -133,6 +133,11 @@ typedef unsigned __int64 uint64_t;
 #  define roundf(arg) floorf((arg) + 0.5f)
 #endif
 
+/* Whether `vsnprintf()` available */
+#if (defined(_MSC_VER) && _MSC_VER < 1900) || defined(ZINT_IS_C89) /* Pre-MSVC 2015 (C++ 14.0) or C89 */
+#define Z_NO_VSNPRINTF
+#endif
+
 /* Is float integral value? (https://stackoverflow.com/a/40404149) */
 #define z_isfintf(arg) (fmodf(arg, 1.0f) == 0.0f)
 
diff --git a/backend/filemem.c b/backend/filemem.c
index 65bfbc7a..37fafa6f 100644
--- a/backend/filemem.c
+++ b/backend/filemem.c
@@ -1,7 +1,7 @@
 /*  filemem.c - write to file/memory abstraction */
 /*
     libzint - the open source barcode library
-    Copyright (C) 2023-2025 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2023-2026 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -84,7 +84,7 @@ static void fm_clear_mem(struct filemem *restrict const fmp) {
         fmp->mem = NULL;
     }
     fmp->memsize = fmp->mempos = fmp->memend = 0;
-#ifdef FM_NO_VSNPRINTF
+#ifdef Z_NO_VSNPRINTF
     if (fmp->fp_null) {
         (void) fclose(fmp->fp_null);
         fmp->fp_null = NULL;
@@ -100,7 +100,7 @@ INTERNAL int zint_fm_open(struct filemem *restrict const fmp, struct zint_symbol
     fmp->memsize = fmp->mempos = fmp->memend = 0;
     fmp->flags = symbol->output_options & (BARCODE_STDOUT | BARCODE_MEMORY_FILE);
     fmp->err = 0;
-#ifdef FM_NO_VSNPRINTF
+#ifdef Z_NO_VSNPRINTF
     fmp->fp_null = NULL;
 #endif
 
@@ -240,7 +240,7 @@ INTERNAL int zint_fm_puts(const char *str, struct filemem *restrict const fmp) {
     return 1;
 }
 
-#ifdef FM_NO_VSNPRINTF
+#ifdef Z_NO_VSNPRINTF
 #  ifdef _WIN32
 #    define DEV_NULL "NUL"
 #  else
@@ -254,14 +254,14 @@ static int fm_vprintf(struct filemem *restrict const fmp, const char *fmt, va_li
     int size, check;
 
     /* Adapted from https://stackoverflow.com/a/52558247/664741 */
-#ifdef FM_NO_VSNPRINTF
+#ifdef Z_NO_VSNPRINTF
     if (!fmp->fp_null && !(fmp->fp_null = fopen(DEV_NULL, "wb"))) {
         return fm_seterr(fmp, errno);
     }
 #endif
 
     va_copy(cpy, ap);
-#ifdef FM_NO_VSNPRINTF
+#ifdef Z_NO_VSNPRINTF
     size = vfprintf(fmp->fp_null, fmt, cpy);
 #else
     size = vsnprintf(NULL, 0, fmt, cpy);
@@ -276,7 +276,7 @@ static int fm_vprintf(struct filemem *restrict const fmp, const char *fmt, va_li
         return 0;
     }
 
-#ifdef FM_NO_VSNPRINTF
+#ifdef Z_NO_VSNPRINTF
     check = vsprintf((char *) fmp->mem + fmp->mempos, fmt, ap);
 #else
     check = vsnprintf((char *) fmp->mem + fmp->mempos, size + 1, fmt, ap);
diff --git a/backend/filemem.h b/backend/filemem.h
index 8509ae36..f096884b 100644
--- a/backend/filemem.h
+++ b/backend/filemem.h
@@ -1,7 +1,7 @@
 /*  filemem.h - write to file/memory abstraction */
 /*
     libzint - the open source barcode library
-    Copyright (C) 2023-2025 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2023-2026 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -40,11 +40,6 @@ extern "C" {
 #include <stdio.h>
 #include "common.h"
 
-/* Whether `vsnprintf()` available */
-#if (defined(_MSC_VER) && _MSC_VER < 1900) || defined(ZINT_IS_C89) /* Pre-MSVC 2015 (C++ 14.0) or C89 */
-#define FM_NO_VSNPRINTF
-#endif
-
 struct filemem {
     FILE *fp;
     unsigned char *mem;
@@ -53,7 +48,7 @@ struct filemem {
     size_t memend;      /* For use by `zint_fm_seek()`, points to highest `mempos` reached */
     int flags;          /* BARCODE_MEMORY_FILE or BARCODE_STDOUT */
     int err;            /* `errno` values, reset only on `zint_fm_open()` */
-#ifdef FM_NO_VSNPRINTF
+#ifdef Z_NO_VSNPRINTF
     FILE *fp_null;      /* Only used for BARCODE_MEMORY_FILE */
 #endif
 };
diff --git a/backend/gs1.c b/backend/gs1.c
index d77136f0..c8643c09 100644
--- a/backend/gs1.c
+++ b/backend/gs1.c
@@ -57,7 +57,7 @@ ZINT_FORMAT_PRINTF(2, 3) static int gs1_err_msg_printf_nochk(char err_msg[50], c
     int size;
     va_start(ap, fmt);
 
-#ifdef ZINT_IS_C89
+#ifdef Z_NO_VSNPRINTF
     size = vsprintf(err_msg, fmt, ap);
 #else
     size = vsnprintf(err_msg, 50, fmt, ap);