diff --git a/backend/common.c b/backend/common.c
index eac8fdb2..4fa00ac7 100644
--- a/backend/common.c
+++ b/backend/common.c
@@ -488,10 +488,7 @@ INTERNAL int set_height(struct zint_symbol *symbol, const float min_row_height,
             row_height = 0.5f;
         }
         if (min_row_height) {
-            /* This seems necessary to get gcc 12.2.1 to work consistently for static 32-bit builds */
-            volatile const float row_height_strip = stripf(row_height);
-            volatile const float min_row_height_strip = stripf(min_row_height);
-            if (row_height_strip < min_row_height_strip) {
+            if (stripf(row_height) < stripf(min_row_height)) {
                 error_number = ZINT_WARN_NONCOMPLIANT;
                 if (!no_errtxt) {
                     strcpy(symbol->errtxt, "247: Height not compliant with standards");
@@ -503,10 +500,7 @@ INTERNAL int set_height(struct zint_symbol *symbol, const float min_row_height,
         symbol->height = stripf(fixed_height); /* Ignore any given height */
     }
     if (max_height) {
-        /* See above */
-        volatile const float symbol_height_strip = stripf(symbol->height);
-        volatile const float max_height_strip = stripf(max_height);
-        if (symbol_height_strip > max_height_strip) {
+        if (stripf(symbol->height) > stripf(max_height)) {
             error_number = ZINT_WARN_NONCOMPLIANT;
             if (!no_errtxt) {
                 strcpy(symbol->errtxt, "248: Height not compliant with standards");
@@ -517,6 +511,13 @@ INTERNAL int set_height(struct zint_symbol *symbol, const float min_row_height,
     return error_number;
 }
 
+/* Prevent inlining of `stripf()` which can optimize away its effect */
+#if defined(__GNUC__) || defined(__clang__)
+__attribute__((__noinline__))
+#endif
+#if defined(_MSC_VER) && _MSC_VER >= 1310 /* MSVC 2003 (VC++ 7.1) */
+__declspec(noinline)
+#endif
 /* Removes excess precision from floats - see https://stackoverflow.com/q/503436 */
 INTERNAL float stripf(const float arg) {
     return *((volatile const float *) &arg);
diff --git a/backend/telepen.c b/backend/telepen.c
index c4fc87f1..e6a526bf 100644
--- a/backend/telepen.c
+++ b/backend/telepen.c
@@ -34,7 +34,7 @@
 /* Telepen Barcode Symbology information and History (BSiH)
    https://telepen.co.uk/wp-content/uploads/2018/10/Barcode-Symbology-information-and-History.pdf */
 
-#define SODIUM_X_F        (IS_NUM_F | IS_UX__F) /* SODIUM "0123456789X" */
+#define SODIUM_X_F        (IS_NUM_F | IS_UX__F | IS_LX__F) /* SODIUM "0123456789Xx" */
 
 #include <stdio.h>
 #include "common.h"
@@ -155,7 +155,7 @@ INTERNAL int telepen_num(struct zint_symbol *symbol, unsigned char source[], int
     int i;
     char dest[521]; /* 12 (start) + 30 * 16 (max for DELs) + 16 (check digit) + 12 (stop) + 1 = 521 */
     char *d = dest;
-    unsigned char temp[64];
+    unsigned char temp[61];
 
     count = 0;
 
@@ -163,20 +163,20 @@ INTERNAL int telepen_num(struct zint_symbol *symbol, unsigned char source[], int
         strcpy(symbol->errtxt, "392: Input too long (60 character maximum)");
         return ZINT_ERROR_TOO_LONG;
     }
-    ustrcpy(temp, source);
-    to_upper(temp, src_len);
-    if (!is_sane(SODIUM_X_F, temp, src_len)) {
+    if (!is_sane(SODIUM_X_F, source, src_len)) {
         strcpy(symbol->errtxt, "393: Invalid character in data (digits and \"X\" only)");
         return ZINT_ERROR_INVALID_DATA;
     }
 
     /* Add a leading zero if required */
     if (src_len & 1) {
-        memmove(temp + 1, temp, src_len);
+        memcpy(temp + 1, source, src_len++);
         temp[0] = '0';
-
-        temp[++src_len] = '\0';
+    } else {
+        memcpy(temp, source, src_len);
     }
+    temp[src_len] = '\0';
+    to_upper(temp, src_len);
 
     /* Start character */
     memcpy(d, TeleTable['_'], 12);
diff --git a/backend/tests/test_telepen.c b/backend/tests/test_telepen.c
index 64cb62e6..495b1ec6 100644
--- a/backend/tests/test_telepen.c
+++ b/backend/tests/test_telepen.c
@@ -27,6 +27,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 #include "testcommon.h"
 
@@ -40,7 +41,7 @@ static void test_large(int index, int debug) {
         int expected_rows;
         int expected_width;
     };
-    // s/\/\*[ 0-9]*\*\//\=printf("\/*%3d*\/", line(".") - line("'<"))
+    /* s/\/\*[ 0-9]*\*\//\=printf("\/\*%3d*\/", line(".") - line("'<")): */
     struct item data[] = {
         /*  0*/ { BARCODE_TELEPEN, "\177", 30, 0, 1, 528 },
         /*  1*/ { BARCODE_TELEPEN, "\177", 31, ZINT_ERROR_TOO_LONG, -1, -1 },
@@ -70,7 +71,7 @@ static void test_large(int index, int debug) {
         ret = ZBarcode_Encode(symbol, (unsigned char *) data_buf, length);
         assert_equal(ret, data[i].ret, "i:%d ZBarcode_Encode ret %d != %d (%s)\n", i, ret, data[i].ret, symbol->errtxt);
 
-        if (ret < 5) {
+        if (ret < ZINT_ERROR) {
             assert_equal(symbol->rows, data[i].expected_rows, "i:%d symbol->rows %d != %d\n", i, symbol->rows, data[i].expected_rows);
             assert_equal(symbol->width, data[i].expected_width, "i:%d symbol->width %d != %d\n", i, symbol->width, data[i].expected_width);
         }
@@ -90,7 +91,7 @@ static void test_hrt(int index, int debug) {
 
         char *expected;
     };
-    // s/\/\*[ 0-9]*\*\//\=printf("\/*%3d*\/", line(".") - line("'<"))
+    /* s/\/\*[ 0-9]*\*\//\=printf("\/\*%3d*\/", line(".") - line("'<")): */
     struct item data[] = {
         /*  0*/ { BARCODE_TELEPEN, "ABC1234.;$", -1, "ABC1234.;$" },
         /*  1*/ { BARCODE_TELEPEN, "abc1234.;$", -1, "abc1234.;$" },
@@ -98,8 +99,8 @@ static void test_hrt(int index, int debug) {
         /*  3*/ { BARCODE_TELEPEN, "ABC\0001234", 8, "ABC 1234" },
         /*  4*/ { BARCODE_TELEPEN_NUM, "1234", -1, "1234" },
         /*  5*/ { BARCODE_TELEPEN_NUM, "123X", -1, "123X" },
-        /*  6*/ { BARCODE_TELEPEN_NUM, "123x", -1, "123X" }, // Converts to upper
-        /*  7*/ { BARCODE_TELEPEN_NUM, "12345", -1, "012345" }, // Adds leading zero if odd
+        /*  6*/ { BARCODE_TELEPEN_NUM, "123x", -1, "123X" }, /* Converts to upper */
+        /*  7*/ { BARCODE_TELEPEN_NUM, "12345", -1, "012345" }, /* Adds leading zero if odd */
     };
     int data_size = ARRAY_SIZE(data);
     int i, length, ret;
@@ -137,7 +138,7 @@ static void test_input(int index, int debug) {
         int expected_rows;
         int expected_width;
     };
-    // s/\/\*[ 0-9]*\*\//\=printf("\/*%3d*\/", line(".") - line("'<"))
+    /* s/\/\*[ 0-9]*\*\//\=printf("\/\*%3d*\/", line(".") - line("'<")): */
     struct item data[] = {
         /*  0*/ { BARCODE_TELEPEN, " !\"#$%&'()*+,-./0123456789:;<", -1, 0, 1, 512 },
         /*  1*/ { BARCODE_TELEPEN, "AZaz\176\001", -1, 0, 1, 144 },
@@ -145,9 +146,9 @@ static void test_input(int index, int debug) {
         /*  3*/ { BARCODE_TELEPEN, "é", -1, ZINT_ERROR_INVALID_DATA, -1, -1 },
         /*  4*/ { BARCODE_TELEPEN_NUM, "1234567890", -1, 0, 1, 128 },
         /*  5*/ { BARCODE_TELEPEN_NUM, "123456789A", -1, ZINT_ERROR_INVALID_DATA, -1, -1 },
-        /*  6*/ { BARCODE_TELEPEN_NUM, "123456789X", -1, 0, 1, 128 }, // [0-9]X allowed
-        /*  7*/ { BARCODE_TELEPEN_NUM, "12345678X9", -1, ZINT_ERROR_INVALID_DATA, -1, -1 }, // X[0-9] not allowed
-        /*  8*/ { BARCODE_TELEPEN_NUM, "1X34567X9X", -1, 0, 1, 128 }, // [0-9]X allowed multiple times
+        /*  6*/ { BARCODE_TELEPEN_NUM, "123456789X", -1, 0, 1, 128 }, /* [0-9]X allowed */
+        /*  7*/ { BARCODE_TELEPEN_NUM, "12345678X9", -1, ZINT_ERROR_INVALID_DATA, -1, -1 }, /* X[0-9] not allowed */
+        /*  8*/ { BARCODE_TELEPEN_NUM, "1X34567X9X", -1, 0, 1, 128 }, /* [0-9]X allowed multiple times */
     };
     int data_size = ARRAY_SIZE(data);
     int i, length, ret;
@@ -167,7 +168,7 @@ static void test_input(int index, int debug) {
         ret = ZBarcode_Encode(symbol, (unsigned char *) data[i].data, length);
         assert_equal(ret, data[i].ret, "i:%d ZBarcode_Encode ret %d != %d (%s)\n", i, ret, data[i].ret, symbol->errtxt);
 
-        if (ret < 5) {
+        if (ret < ZINT_ERROR) {
             assert_equal(symbol->rows, data[i].expected_rows, "i:%d symbol->rows %d != %d\n", i, symbol->rows, data[i].expected_rows);
             assert_equal(symbol->width, data[i].expected_width, "i:%d symbol->width %d != %d\n", i, symbol->width, data[i].expected_width);
         }
@@ -178,8 +179,10 @@ static void test_input(int index, int debug) {
     testFinish();
 }
 
-// Telepen Barcode Symbology information and History (BSiH) https://telepen.co.uk/wp-content/uploads/2018/10/Barcode-Symbology-information-and-History.pdf
-// E2326U: SB Telepen Barcode Fonts Guide Issue 2 (Apr 2009) https://telepen.co.uk/wp-content/uploads/2018/09/SB-Telepen-Barcode-Fonts-V2.pdf
+/* Telepen Barcode Symbology information and History (BSiH)
+     https://telepen.co.uk/wp-content/uploads/2018/10/Barcode-Symbology-information-and-History.pdf */
+/* E2326U: SB Telepen Barcode Fonts Guide Issue 2 (Apr 2009)
+     https://telepen.co.uk/wp-content/uploads/2018/09/SB-Telepen-Barcode-Fonts-V2.pdf */
 static void test_encode(int index, int generate, int debug) {
 
     struct item {
@@ -233,7 +236,7 @@ static void test_encode(int index, int generate, int debug) {
     char bwipp_buf[8192];
     char bwipp_msg[1024];
 
-    int do_bwipp = (debug & ZINT_DEBUG_TEST_BWIPP) && testUtilHaveGhostscript(); // Only do BWIPP test if asked, too slow otherwise
+    int do_bwipp = (debug & ZINT_DEBUG_TEST_BWIPP) && testUtilHaveGhostscript(); /* Only do BWIPP test if asked, too slow otherwise */
 
     testStart("test_encode");
 
@@ -256,7 +259,7 @@ static void test_encode(int index, int generate, int debug) {
             testUtilModulesPrint(symbol, "                    ", "\n");
             printf("                },\n");
         } else {
-            if (ret < 5) {
+            if (ret < ZINT_ERROR) {
                 int width, row;
 
                 assert_equal(symbol->rows, data[i].expected_rows, "i:%d symbol->rows %d != %d (%s)\n", i, symbol->rows, data[i].expected_rows, data[i].data);
@@ -282,7 +285,7 @@ static void test_encode(int index, int generate, int debug) {
     testFinish();
 }
 
-// #181 Nico Gunkel OSS-Fuzz
+/* #181 Nico Gunkel OSS-Fuzz */
 static void test_fuzz(int index, int debug) {
 
     struct item {
@@ -291,16 +294,17 @@ static void test_fuzz(int index, int debug) {
         int length;
         int ret;
     };
-    // Note NULs where using DELs code (16 binary characters wide)
-    // s/\/\*[ 0-9]*\*\//\=printf("\/*%2d*\/", line(".") - line("'<"))
+    /* Note NULs where using DELs code (16 binary characters wide) */
+    /* s/\/\*[ 0-9]*\*\//\=printf("\/\*%3d*\/", line(".") - line("'<")): */
     struct item data[] = {
-        /* 0*/ { BARCODE_TELEPEN, "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000", 30, 0 },
-        /* 1*/ { BARCODE_TELEPEN, "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000", 31, ZINT_ERROR_TOO_LONG },
-        /* 2*/ { BARCODE_TELEPEN_NUM, "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000", 60, ZINT_ERROR_INVALID_DATA },
-        /* 3*/ { BARCODE_TELEPEN_NUM, "040404040404040404040404040404040404040404040404040404040404", 60, 0 },
-        /* 4*/ { BARCODE_TELEPEN_NUM, "1234567890123456789012345678901234567890123456789012345678901", 61, ZINT_ERROR_TOO_LONG },
-        /* 5*/ { BARCODE_TELEPEN_NUM, "00000000000000000000000000000000000000000000000000000000000X", 60, 0 },
-        /* 6*/ { BARCODE_TELEPEN_NUM, "999999999999999999999999999999999999999999999999999999999999", 60, 0 },
+        /*  0*/ { BARCODE_TELEPEN, "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000", 30, 0 },
+        /*  1*/ { BARCODE_TELEPEN, "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000", 31, ZINT_ERROR_TOO_LONG },
+        /*  2*/ { BARCODE_TELEPEN_NUM, "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000", 60, ZINT_ERROR_INVALID_DATA },
+        /*  3*/ { BARCODE_TELEPEN_NUM, "040404040404040404040404040404040404040404040404040404040404", 60, 0 },
+        /*  4*/ { BARCODE_TELEPEN_NUM, "1234567890123456789012345678901234567890123456789012345678901", 61, ZINT_ERROR_TOO_LONG },
+        /*  5*/ { BARCODE_TELEPEN_NUM, "00000000000000000000000000000000000000000000000000000000000X", 60, 0 },
+        /*  6*/ { BARCODE_TELEPEN_NUM, "999999999999999999999999999999999999999999999999999999999999", 60, 0 },
+        /*  7*/ { BARCODE_TELEPEN_NUM, "1234567890123456789012345678901234567890123456789012345678901234567890", 4, 0 }, /* Length given, strlen > 61, so pseudo not NUL-terminated */
     };
     int data_size = ARRAY_SIZE(data);
     int i, length, ret;
@@ -365,7 +369,7 @@ static const char TeleTable[128][16] = {
     {'1','1','1','1','1','1','1','1','1','1','1','1','1','1','1','1'},
 };
 
-// Dummy to generate lengths table
+/* Dummy to generate lengths table */
 static void test_generate_lens(int generate) {
 
     int i;