diff --git a/src/common/backend/utils/adt/formatting.cpp b/src/common/backend/utils/adt/formatting.cpp
index b59afda08..4b9ea9451 100644
--- a/src/common/backend/utils/adt/formatting.cpp
+++ b/src/common/backend/utils/adt/formatting.cpp
@@ -3698,19 +3698,55 @@ static void DCH_to_char(FormatNode* node, bool is_interval, TmToChar* in, char*
                 s += strlen(s);
                 break;
             case DCH_RM:
-                if (!tm->tm_mon)
-                    break;
-                rc = sprintf_s(s, len, "%*s", S_FM(n->suffix) ? 0 : -4, rm_months_upper[MONTHS_PER_YEAR - tm->tm_mon]);
-                securec_check_ss(rc, "\0", "\0");
-                s += strlen(s);
-                break;
             case DCH_rm:
-                if (!tm->tm_mon)
+                /*
+                * For intervals, values like '12 month' will be reduced to 0
+                * month and some years.  These should be processed.
+                */
+                if (!tm->tm_mon && !tm->tm_year) {
                     break;
-                rc = sprintf_s(s, len, "%*s", S_FM(n->suffix) ? 0 : -4, rm_months_lower[MONTHS_PER_YEAR - tm->tm_mon]);
-                securec_check_ss(rc, "\0", "\0");
-                s += strlen(s);
-                break;
+                } else {
+                    int mon = 0;
+                    char** months = NULL;
+
+                    if (n->key->id == DCH_RM) {
+                        months = rm_months_upper;
+                    } else {
+                        months = rm_months_lower;
+                    }
+
+                    /*
+                    * Compute the position in the roman-numeral array.  Note
+                    * that the contents of the array are reversed, December
+                    * being first and January last.
+                    */
+                    if (tm->tm_mon == 0) {
+                        /*
+                        * This case is special, and tracks the case of full
+                        * interval years.
+                        */
+                        mon = tm->tm_year >= 0 ? 0 : MONTHS_PER_YEAR - 1;
+                    } else if (tm->tm_mon < 0) {
+                        /*
+                        * Negative case.  In this case, the calculation is
+                        * reversed, where -1 means December, -2 November,
+                        * etc.
+                        */
+                        mon = -1 * (tm->tm_mon + 1);
+                    } else {
+                        /*
+                        * Common case, with a strictly positive value.  The
+                        * position in the array matches with the value of
+                        * tm_mon.
+                        */
+                        mon = MONTHS_PER_YEAR - tm->tm_mon;
+                    }
+
+                    rc = sprintf_s(s, len, "%*s", S_FM(n->suffix) ? 0 : -4, months[mon]);
+                    securec_check_ss(rc, "\0", "\0");
+                    s += strlen(s);
+                    break;
+                }
             case DCH_W:
                 rc = sprintf_s(s, len, "%d", (tm->tm_mday - 1) / 7 + 1);
                 securec_check_ss(rc, "\0", "\0");