diff --git a/usr.bin/sort/bwstring.c b/usr.bin/sort/bwstring.c
--- a/usr.bin/sort/bwstring.c
+++ b/usr.bin/sort/bwstring.c
@@ -43,63 +43,94 @@
 
 bool byte_sort;
 
-static wchar_t **wmonths;
-static char **cmonths;
+struct wmonth {
+	wchar_t *mon;
+	wchar_t *ab;
+	wchar_t *alt;
+};
+
+struct cmonth {
+	char *mon;
+	char *ab;
+	char *alt;
+};
+
+static struct wmonth *wmonths;
+static struct cmonth *cmonths;
 
 /* initialise months */
 
 void
 initialise_months(void)
 {
-	const nl_item item[12] = { ABMON_1, ABMON_2, ABMON_3, ABMON_4,
+	const nl_item mon_item[12] = { MON_1, MON_2, MON_3, MON_4,
+	    MON_5, MON_6, MON_7, MON_8, MON_9, MON_10,
+	    MON_11, MON_12 };
+	const nl_item ab_item[12] = { ABMON_1, ABMON_2, ABMON_3, ABMON_4,
 	    ABMON_5, ABMON_6, ABMON_7, ABMON_8, ABMON_9, ABMON_10,
 	    ABMON_11, ABMON_12 };
+	const nl_item alt_item[12] = { ALTMON_1, ALTMON_2, ALTMON_3, ALTMON_4,
+	    ALTMON_5, ALTMON_6, ALTMON_7, ALTMON_8, ALTMON_9, ALTMON_10,
+	    ALTMON_11, ALTMON_12 };
 	char *tmp;
 	size_t len;
 
+	/*
+	 * Handle all possible month formats: abbrevation, full month name,
+	 * standalone month name (without case ending).
+	 */
 	if (mb_cur_max == 1) {
 		if (cmonths == NULL) {
-			char *m;
+			struct cmonth m;
 
-			cmonths = sort_malloc(sizeof(char*) * 12);
+			cmonths = sort_malloc(sizeof(struct cmonth) * 12);
 			for (int i = 0; i < 12; i++) {
-				cmonths[i] = NULL;
-				tmp = nl_langinfo(item[i]);
-				if (debug_sort)
-					printf("month[%d]=%s\n", i, tmp);
-				if (*tmp == '\0')
-					continue;
-				m = sort_strdup(tmp);
-				len = strlen(tmp);
-				for (unsigned int j = 0; j < len; j++)
-					m[j] = toupper(m[j]);
-				cmonths[i] = m;
+#define POPULATE(field) do {					\
+	tmp = nl_langinfo(field##_item[i]);			\
+	if (debug_sort)						\
+		printf("month[%d]=%s\n", i, tmp);		\
+	if (*tmp == '\0')					\
+		continue;					\
+	m.field = sort_strdup(tmp);				\
+	len = strlen(tmp);					\
+	for (unsigned int j = 0; j < len; j++)			\
+		m.field[j] = toupper(m.field[j]);		\
+	cmonths[i].field = m.field;				\
+} while (0)
+				POPULATE(mon);
+				POPULATE(ab);
+				POPULATE(alt);
+#undef POPULATE
 			}
 		}
 
 	} else {
 		if (wmonths == NULL) {
-			wchar_t *m;
+			struct wmonth m;
 
-			wmonths = sort_malloc(sizeof(wchar_t *) * 12);
+			wmonths = sort_malloc(sizeof(struct wmonth) * 12);
 			for (int i = 0; i < 12; i++) {
-				wmonths[i] = NULL;
-				tmp = nl_langinfo(item[i]);
-				if (debug_sort)
-					printf("month[%d]=%s\n", i, tmp);
-				if (*tmp == '\0')
-					continue;
-				len = strlen(tmp);
-				m = sort_malloc(SIZEOF_WCHAR_STRING(len + 1));
-				if (mbstowcs(m, tmp, len) ==
-				    ((size_t) - 1)) {
-					sort_free(m);
-					continue;
-				}
-				m[len] = L'\0';
-				for (unsigned int j = 0; j < len; j++)
-					m[j] = towupper(m[j]);
-				wmonths[i] = m;
+#define POPULATE(field) do {					\
+	tmp = nl_langinfo(field##_item[i]);			\
+	if (debug_sort)						\
+		printf("month[%d]=%s\n", i, tmp);		\
+	if (*tmp == '\0')					\
+		continue;					\
+	len = strlen(tmp);					\
+	m.field = sort_malloc(SIZEOF_WCHAR_STRING(len + 1));	\
+	if (mbstowcs(m.field, tmp, len) == ((size_t) - 1)) {	\
+		sort_free(m.field);				\
+		continue;					\
+	}							\
+	m.field[len] = L'\0';					\
+	for (unsigned int j = 0; j < len; j++)			\
+		m.field[j] = towupper(m.field[j]);		\
+	wmonths[i].field = m.field;				\
+} while (0)
+				POPULATE(mon);
+				POPULATE(ab);
+				POPULATE(alt);
+#undef POPULATE
 			}
 		}
 	}
@@ -754,8 +785,11 @@
 			++s;
 
 		for (int i = 11; i >= 0; --i) {
-			if (cmonths[i] &&
-			    (s == strstr(s, cmonths[i])))
+			if (cmonths[i].mon && (s == strstr(s, cmonths[i].mon)))
+				return (i);
+			if (cmonths[i].ab && (s == strstr(s, cmonths[i].ab)))
+				return (i);
+			if (cmonths[i].alt && (s == strstr(s, cmonths[i].alt)))
 				return (i);
 		}
 
@@ -769,7 +803,11 @@
 			++s;
 
 		for (int i = 11; i >= 0; --i) {
-			if (wmonths[i] && (s == wcsstr(s, wmonths[i])))
+			if (wmonths[i].ab && (s == wcsstr(s, wmonths[i].ab)))
+				return (i);
+			if (wmonths[i].mon && (s == wcsstr(s, wmonths[i].mon)))
+				return (i);
+			if (wmonths[i].alt && (s == wcsstr(s, wmonths[i].alt)))
 				return (i);
 		}
 	}