diff --git a/mysql-test/main/mdev_38791.result b/mysql-test/main/mdev_38791.result
new file mode 100644
index 0000000000000..42d480b4d0869
--- /dev/null
+++ b/mysql-test/main/mdev_38791.result
@@ -0,0 +1,11 @@
+SET sql_mode='ORACLE';
+SELECT TO_DATE('Monday Mon', 'DAY DY');
+TO_DATE('Monday Mon', 'DAY DY')
+NULL
+Warnings:
+Warning	1411	Incorrect datetime value: 'Monday Mon' for function to_date
+SELECT TO_DATE('Mon Mon', 'DY DY');
+TO_DATE('Mon Mon', 'DY DY')
+NULL
+Warnings:
+Warning	1411	Incorrect datetime value: 'Mon Mon' for function to_date
diff --git a/mysql-test/main/mdev_38791.test b/mysql-test/main/mdev_38791.test
new file mode 100644
index 0000000000000..2ecd54da3aed2
--- /dev/null
+++ b/mysql-test/main/mdev_38791.test
@@ -0,0 +1,4 @@
+SET sql_mode='ORACLE';
+
+SELECT TO_DATE('Monday Mon', 'DAY DY');
+SELECT TO_DATE('Mon Mon', 'DY DY');
diff --git a/sql/item_timefunc.cc b/sql/item_timefunc.cc
index c008c2089ba29..0cb00124df96b 100644
--- a/sql/item_timefunc.cc
+++ b/sql/item_timefunc.cc
@@ -2982,6 +2982,8 @@ static bool parse_format_string(const String *format, uint16 *fmt_array,
       }
       else if (tmp1 == 'Y')
       {
+        if (for_to_date && formats_used(&used, FMT_DAY))
+          goto error;
         *tmp_fmt= FMT_DY;                       // Day name
         tmp_len+= 3;
         type_flags|= PARSE_TYPE_WEEKDAY | PARSE_TYPE_NON_DETERMINISTIC;
@@ -2990,6 +2992,8 @@ static bool parse_format_string(const String *format, uint16 *fmt_array,
       {
         if (ptr + 2 == end || my_toupper(system_charset_info, *(ptr+2)) != 'Y')
           goto error;
+        if (for_to_date && formats_used(&used, FMT_DAY))
+          goto error;
         *tmp_fmt= FMT_DAY;                      // Day name
         tmp_len+= locale->max_day_name_length * my_charset_utf8mb3_bin.mbmaxlen;
         type_flags|= PARSE_TYPE_WEEKDAY | PARSE_TYPE_NON_DETERMINISTIC;