diff --git a/backend/code128.c b/backend/code128.c
index c82ac2d6..422a77df 100644
--- a/backend/code128.c
+++ b/backend/code128.c
@@ -1180,8 +1180,6 @@ INTERNAL int dpd(struct zint_symbol *symbol, unsigned char source[], int length)
     return error_number;
 }
 
-INTERNAL int iso3166_alpha2(const char *cc); /* In "iso3166.h" which is included by "gs1.c" */
-
 /* Universal Postal Union S10 */
 /* https://www.upu.int/UPU/media/upu/files/postalSolutions/programmesAndServices/standards/S10-12.pdf */
 INTERNAL int upu_s10(struct zint_symbol *symbol, unsigned char source[], int length) {
@@ -1247,7 +1245,7 @@ INTERNAL int upu_s10(struct zint_symbol *symbol, unsigned char source[], int len
     } else if (strchr("FHIOXY", local_source[0]) != NULL) { /* These aren't allocated as of spec Oct 2017 */
         strcpy(symbol->errtxt, "840: Non-standard Service Indicator (first 2 characters)");
         error_number = ZINT_WARN_NONCOMPLIANT;
-    } else if (!iso3166_alpha2((const char *) (local_source + 11))) {
+    } else if (!gs1_iso3166_alpha2(local_source + 11)) {
         strcpy(symbol->errtxt, "841: Country code (last two characters) is not ISO 3166-1");
         error_number = ZINT_WARN_NONCOMPLIANT;
     }
diff --git a/backend/gs1.c b/backend/gs1.c
index ac12c181..0de6c79c 100644
--- a/backend/gs1.c
+++ b/backend/gs1.c
@@ -1428,4 +1428,9 @@ INTERNAL char gs1_check_digit(const unsigned char source[], const int length) {
     return itoc((10 - (count % 10)) % 10);
 }
 
+/* Helper to expose `iso3166_alpha2()` */
+INTERNAL int gs1_iso3166_alpha2(const unsigned char *cc) {
+    return iso3166_alpha2((const char *) cc);
+}
+
 /* vim: set ts=4 sw=4 et : */
diff --git a/backend/gs1.h b/backend/gs1.h
index 9e3857f7..d895d3d0 100644
--- a/backend/gs1.h
+++ b/backend/gs1.h
@@ -40,6 +40,7 @@ extern "C" {
 INTERNAL int gs1_verify(struct zint_symbol *symbol, const unsigned char source[], const int src_len,
                 unsigned char reduced[]);
 INTERNAL char gs1_check_digit(const unsigned char source[], const int src_len);
+INTERNAL int gs1_iso3166_alpha2(const unsigned char *cc);
 
 #ifdef __cplusplus
 }
diff --git a/backend/iso3166.h b/backend/iso3166.h
index a37525d2..fda673b3 100644
--- a/backend/iso3166.h
+++ b/backend/iso3166.h
@@ -62,7 +62,7 @@ static int iso3166_numeric(int cc) {
 }
 
 /* Whether ISO 3166-1 alpha2 */
-INTERNAL int iso3166_alpha2(const char *cc) {
+static int iso3166_alpha2(const char *cc) {
     static const unsigned char codes[85] = {
         0x78, 0x59, 0xDF, 0xEE, 0xEF, 0xBD, 0xDD, 0xDE,
         0x27, 0x3F, 0x84, 0x15, 0x80, 0xD4, 0x00, 0x0E,
diff --git a/backend_tcl/zint.c b/backend_tcl/zint.c
index b2f75afa..5b52a7ae 100644
--- a/backend_tcl/zint.c
+++ b/backend_tcl/zint.c
@@ -162,6 +162,8 @@
 - Added MAILMARK_2D
 - Renamed MAILMARK to MAILMARK_4S
     *** Potential incompatibility ***
+2022-12-09 GL
+- Added UPU_S10
 */
 
 #if defined(__WIN32__) || defined(_WIN32) || defined(WIN32)
@@ -308,6 +310,7 @@ static const char *s_code_list[] = {
     "DotCode",
     "HanXin",
     "MailMark-2D",
+    "UPU-S10",
     "MailMark-4S",
     "AztecRunes",
     "Code32",
@@ -409,6 +412,7 @@ static const int s_code_number[] = {
     BARCODE_DOTCODE,
     BARCODE_HANXIN,
     BARCODE_MAILMARK_2D,
+    BARCODE_UPU_S10,
     BARCODE_MAILMARK_4S,
     BARCODE_AZRUNE,
     BARCODE_CODE32,