diff --git a/src/sas/readstat_sas7bdat_read.c b/src/sas/readstat_sas7bdat_read.c
index 8b804353..3bf11581 100644
--- a/src/sas/readstat_sas7bdat_read.c
+++ b/src/sas/readstat_sas7bdat_read.c
@@ -746,14 +746,36 @@ static readstat_error_t sas7bdat_construct_format(char *dst, size_t dst_len,
     if (retval != READSTAT_OK)
         return retval;
 
-    size_t len = strlen(dst);
-    if (width && len < dst_len - 1) {
-        snprintf(dst + len, dst_len - len, "%d", width);
-        len = strlen(dst);
+    /* Digits require a width */
+    if (width == 0 && digits != 0)
+        return READSTAT_ERROR_PARSE;
+
+    if (strchr(dst, '.')) {
+        /* Legacy layout: earlier ReadStat writers stored the full format
+         * string (e.g. "YYMMDD10." or "BEST.") verbatim as the name, with
+         * width and digits both 0. Return it unchanged. */
+        if (width == 0 && digits == 0)
+            return READSTAT_OK;
+        return READSTAT_ERROR_PARSE;
     }
-    if (len && digits && len < dst_len - 1) {
-        snprintf(dst + len, dst_len - len, ".%d", digits);
+
+    /* No format at all */
+    if (dst[0] == '\0' && width == 0)
+        return READSTAT_OK;
+
+    /* NAME. / NAMEw. / NAMEw.d (NAME may be empty, as in the w.d format) */
+    size_t len = strlen(dst);
+    int written;
+    if (digits) {
+        written = snprintf(dst + len, dst_len - len, "%d.%d", width, digits);
+    } else if (width) {
+        written = snprintf(dst + len, dst_len - len, "%d.", width);
+    } else {
+        written = snprintf(dst + len, dst_len - len, ".");
     }
+    if (written < 0 || (size_t)written >= dst_len - len)
+        return READSTAT_ERROR_PARSE;
+
     return READSTAT_OK;
 }
 
diff --git a/src/sas/readstat_sas7bdat_write.c b/src/sas/readstat_sas7bdat_write.c
index f5e8c011..943dc373 100644
--- a/src/sas/readstat_sas7bdat_write.c
+++ b/src/sas/readstat_sas7bdat_write.c
@@ -366,34 +366,26 @@ static readstat_error_t sas7bdat_text_add(sas7bdat_write_ctx_t *ctx, const char
 /* Formats -------------------------------------------------------------- */
 
 /* Splits a format such as "DATETIME19.2" into name "DATETIME", width 19 and
- * 2 digits, the way SAS stores it. If the string can't be split without
- * losing information, it is stored verbatim as the format name. */
-static void sas7bdat_split_format(const char *format, char *name, size_t name_len,
+ * 2 digits, the way SAS stores it. */
+static readstat_error_t sas7bdat_split_format(const char *format, char *name, size_t name_len,
         uint16_t *width, uint16_t *digits) {
     name[0] = '\0';
     *width = 0;
     *digits = 0;
     if (format == NULL || format[0] == '\0')
-        return;
+        return READSTAT_OK;
 
     xport_format_t parsed;
-    if (xport_parse_format(format, strlen(format), &parsed, NULL, NULL) == READSTAT_OK &&
-            parsed.width >= 0 && parsed.width <= UINT16_MAX &&
-            parsed.decimals >= 0 && parsed.decimals <= UINT16_MAX) {
-        char rebuilt[64];
-        size_t len = snprintf(rebuilt, sizeof(rebuilt), "%s", parsed.name);
-        if (parsed.width && len < sizeof(rebuilt))
-            len += snprintf(rebuilt + len, sizeof(rebuilt) - len, "%d", parsed.width);
-        if (parsed.decimals && len < sizeof(rebuilt))
-            len += snprintf(rebuilt + len, sizeof(rebuilt) - len, ".%d", parsed.decimals);
-        if (len < sizeof(rebuilt) && strcmp(rebuilt, format) == 0) {
-            snprintf(name, name_len, "%s", parsed.name);
-            *width = parsed.width;
-            *digits = parsed.decimals;
-            return;
-        }
-    }
-    snprintf(name, name_len, "%s", format);
+    if (xport_parse_format(format, strlen(format), &parsed, NULL, NULL) != READSTAT_OK ||
+            parsed.width < 0 || parsed.width > UINT16_MAX ||
+            parsed.decimals < 0 || parsed.decimals > UINT16_MAX ||
+            (parsed.width == 0 && parsed.decimals != 0))
+        return READSTAT_ERROR_BAD_FORMAT_STRING;
+
+    snprintf(name, name_len, "%s", parsed.name);
+    *width = parsed.width;
+    *digits = parsed.decimals;
+    return READSTAT_OK;
 }
 
 /* Column name hash table ----------------------------------------------- */
@@ -528,10 +520,12 @@ static readstat_error_t sas7bdat_add_column_text(readstat_writer_t *writer, sas7
         size_t name_len = strlen(variable->name);
         size_t label_len = strlen(variable->label);
 
-        sas7bdat_split_format(variable->format, format_name, sizeof(format_name),
-                &ctx->format_widths[i], &ctx->format_digits[i]);
-        sas7bdat_split_format(variable->informat, informat_name, sizeof(informat_name),
-                &ctx->informat_widths[i], &ctx->informat_digits[i]);
+        if ((retval = sas7bdat_split_format(variable->format, format_name, sizeof(format_name),
+                        &ctx->format_widths[i], &ctx->format_digits[i])) != READSTAT_OK)
+            goto cleanup;
+        if ((retval = sas7bdat_split_format(variable->informat, informat_name, sizeof(informat_name),
+                        &ctx->informat_widths[i], &ctx->informat_digits[i])) != READSTAT_OK)
+            goto cleanup;
 
         if ((retval = sas7bdat_text_add(ctx, variable->name, &ctx->name_refs[i])) != READSTAT_OK)
             goto cleanup;
diff --git a/src/sas/readstat_xport.h b/src/sas/readstat_xport.h
index 2a2e3f7d..c3e2c7c3 100644
--- a/src/sas/readstat_xport.h
+++ b/src/sas/readstat_xport.h
@@ -36,7 +36,7 @@ typedef struct xport_namestr_s {
 #pragma pack(pop)
 
 typedef struct xport_format_s {
-    char         name[32];
+    char         name[33];
     int          width;
     int          decimals;
 } xport_format_t;
diff --git a/src/test/test_list.h b/src/test/test_list.h
index b24944c4..902936ff 100644
--- a/src/test/test_list.h
+++ b/src/test/test_list.h
@@ -812,26 +812,26 @@ static rt_test_group_t _test_groups[] = {
                 .test_formats = RT_FORMAT_SAS7BDAT,
                 .rows = 0,
                 .columns = {
-                    { .name = "one_of_many_long_column_names_1", .label = "Label for column 1", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_2", .label = "Label for column 2", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_3", .label = "Label for column 3", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_4", .label = "Label for column 4", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_5", .label = "Label for column 5", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_6", .label = "Label for column 6", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_7", .label = "Label for column 7", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_8", .label = "Label for column 8", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_9", .label = "Label for column 9", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_10", .label = "Label for column 10", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_11", .label = "Label for column 11", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_12", .label = "Label for column 12", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_13", .label = "Label for column 13", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_14", .label = "Label for column 14", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_15", .label = "Label for column 15", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_16", .label = "Label for column 16", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_17", .label = "Label for column 17", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_18", .label = "Label for column 18", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_19", .label = "Label for column 19", .format = "$CHAR8", .type = READSTAT_TYPE_STRING },
-                    { .name = "one_of_many_long_column_names_20", .label = "Label for column 20", .format = "$CHAR8", .type = READSTAT_TYPE_STRING }
+                    { .name = "one_of_many_long_column_names_1", .label = "Label for column 1", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_2", .label = "Label for column 2", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_3", .label = "Label for column 3", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_4", .label = "Label for column 4", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_5", .label = "Label for column 5", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_6", .label = "Label for column 6", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_7", .label = "Label for column 7", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_8", .label = "Label for column 8", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_9", .label = "Label for column 9", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_10", .label = "Label for column 10", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_11", .label = "Label for column 11", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_12", .label = "Label for column 12", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_13", .label = "Label for column 13", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_14", .label = "Label for column 14", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_15", .label = "Label for column 15", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_16", .label = "Label for column 16", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_17", .label = "Label for column 17", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_18", .label = "Label for column 18", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_19", .label = "Label for column 19", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING },
+                    { .name = "one_of_many_long_column_names_20", .label = "Label for column 20", .format = "$CHAR8.", .type = READSTAT_TYPE_STRING }
                 }
             }
         }
@@ -1482,6 +1482,22 @@ static rt_test_group_t _test_groups[] = {
                     { .name = "VAR2", .type = READSTAT_TYPE_STRING, .format = "$CHAR3.", .label_set = "$CHAR3." }
                 }
             },
+            {
+                .label = "SAS7BDAT format without width",
+                .test_formats = RT_FORMAT_SAS7BDAT,
+                .columns = {
+                    { .name = "VAR1", .type = READSTAT_TYPE_DOUBLE, .format = "DOLLAR.", .informat = "BEST." },
+                    { .name = "VAR2", .type = READSTAT_TYPE_STRING, .format = "$UPCASE.", .informat = "$CHAR." },
+                }
+            },
+            {
+                .label = "SAS 32-character format names",
+                .test_formats = RT_FORMAT_SAS7BDAT | RT_FORMAT_XPORT_8,
+                .columns = {
+                    { .name = "VAR1", .type = READSTAT_TYPE_DOUBLE, .format = "ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEF12.2" },
+                    { .name = "VAR2", .type = READSTAT_TYPE_STRING, .format = "$ABCDEFGHIJKLMNOPQRSTUVWXYZABCDE8." },
+                }
+            },
             {
                 .label = "SAS informats",
                 .test_formats = RT_FORMAT_SAS7BDAT | RT_FORMAT_XPORT_8,
@@ -1509,14 +1525,44 @@ static rt_test_group_t _test_groups[] = {
                 }
             },
             {
-                .label = "XPT bad formats",
+                .label = "SAS format with two dots",
                 .write_error = READSTAT_ERROR_BAD_FORMAT_STRING,
-                .test_formats = RT_FORMAT_XPORT_5 | RT_FORMAT_XPORT_8,
+                .test_formats = RT_FORMAT_SAS,
+                .columns = {
+                    { .name = "VAR1", .type = READSTAT_TYPE_DOUBLE, .format = "10.3.", .label_set = "10.3." }
+                }
+            },
+            {
+                .label = "SAS character format with digits",
+                .write_error = READSTAT_ERROR_BAD_FORMAT_STRING,
+                .test_formats = RT_FORMAT_SAS,
+                .columns = {
+                    { .name = "VAR2", .type = READSTAT_TYPE_STRING, .format = "$CHAR3.1", .label_set = "$CHAR3.1" }
+                }
+            },
+            {
+                .label = "SAS format with negative digits",
+                .write_error = READSTAT_ERROR_BAD_FORMAT_STRING,
+                .test_formats = RT_FORMAT_SAS,
                 .columns = {
-                    { .name = "VAR1", .type = READSTAT_TYPE_DOUBLE, .format = "10.3.", .label_set = "10.3." },
-                    { .name = "VAR2", .type = READSTAT_TYPE_STRING, .format = "$CHAR3.1", .label_set = "$CHAR3.1" },
                     { .name = "VAR3", .type = READSTAT_TYPE_DOUBLE, .format = "YYQ-1", .label_set = "YYQ-1" }
                 }
+            },
+            {
+                .label = "SAS7BDAT format with digits but no width",
+                .write_error = READSTAT_ERROR_BAD_FORMAT_STRING,
+                .test_formats = RT_FORMAT_SAS7BDAT,
+                .columns = {
+                    { .name = "VAR1", .type = READSTAT_TYPE_DOUBLE, .format = ".2", .label_set = ".2" }
+                }
+            },
+            {
+                .label = "Too long SAS7BDAT format name",
+                .write_error = READSTAT_ERROR_BAD_FORMAT_STRING,
+                .test_formats = RT_FORMAT_SAS7BDAT,
+                .columns = {
+                    { .name = "VAR1", .type = READSTAT_TYPE_DOUBLE, .format = "ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFG12.2" }
+                }
             }
         }
     },
@@ -3652,7 +3698,8 @@ static rt_test_group_t _test_groups[] = {
                 .columns = {
                     {
                         .name = "Date1",
-                        .informat = "F8",
+                        .format = "YYMMDD10.",
+                        .informat = "F8.",
                         .type = READSTAT_TYPE_DOUBLE,
                         .values = { 
                             { .type = READSTAT_TYPE_DOUBLE, .v = { .double_value = 5 } },
@@ -3662,7 +3709,8 @@ static rt_test_group_t _test_groups[] = {
                     },
                     {
                         .name = "Date2",
-                        .informat = "F8",
+                        .format = "DATE7.",
+                        .informat = "F8.",
                         .type = READSTAT_TYPE_DOUBLE,
                         .values = { 
                             { .type = READSTAT_TYPE_DOUBLE, .v = { .double_value = 3 } },
@@ -3672,7 +3720,8 @@ static rt_test_group_t _test_groups[] = {
                     },
                     {
                         .name = "DateTime",
-                        .informat = "DATETIME19",
+                        .format = "DATETIME19.",
+                        .informat = "DATETIME19.",
                         .type = READSTAT_TYPE_DOUBLE,
                         .values = { 
                             { .type = READSTAT_TYPE_DOUBLE, .v = { .double_value = -8907752836 } },
@@ -3682,6 +3731,7 @@ static rt_test_group_t _test_groups[] = {
                     },
                     {
                         .name = "DateTimeHi",
+                        .format = "DATETIME28.9",
                         .informat = "23.9",
                         .type = READSTAT_TYPE_DOUBLE,
                         .values = { 
@@ -3692,7 +3742,8 @@ static rt_test_group_t _test_groups[] = {
                     },
                     {
                         .name = "Taiw",
-                        .informat = "F8",
+                        .format = "MINGUO10.",
+                        .informat = "F8.",
                         .type = READSTAT_TYPE_DOUBLE,
                         .values = { 
                             { .type = READSTAT_TYPE_DOUBLE, .v = { .double_value = -17532 } },
diff --git a/src/test/test_types.h b/src/test/test_types.h
index 7cd2af83..d41311e3 100644
--- a/src/test/test_types.h
+++ b/src/test/test_types.h
@@ -9,7 +9,7 @@
 #define RT_MAX_VALUE_LABELS          4
 #define RT_MAX_STRING               96
 #define RT_MAX_VALUE_LABEL_STRING  121
-#define MAX_TESTS_PER_GROUP 20
+#define MAX_TESTS_PER_GROUP         22
 
 
 typedef struct rt_label_set_s {