diff --git a/src/backend/utils/adt/datetime.c b/src/backend/utils/adt/datetime.c
index a3cfd54409b..cebc1172744 100644
--- a/src/backend/utils/adt/datetime.c
+++ b/src/backend/utils/adt/datetime.c
@@ -3365,7 +3365,7 @@ DecodeInterval(char **field, int *ftype, int nf, int range,
 	 * to dump in postgres style, not SQL style.)
 	 *----------
 	 */
-	if (IntervalStyle == INTSTYLE_SQL_STANDARD && *field[0] == '-')
+	if (IntervalStyle == INTSTYLE_SQL_STANDARD && nf > 0 && *field[0] == '-')
 	{
 		force_negative = true;
 		/* Check for additional explicit signs */
diff --git a/src/test/regress/expected/interval.out b/src/test/regress/expected/interval.out
index 00885acd1df..78c1fab2b63 100644
--- a/src/test/regress/expected/interval.out
+++ b/src/test/regress/expected/interval.out
@@ -857,6 +857,11 @@ SELECT  interval '-23 hours 45 min 12.34 sec',
  -23:45:12.34 | -1 23:45:12.34 | -1-2 -1 -23:45:12.34 | -0-10 +1 +23:45:12.34
 (1 row)
 
+-- edge case for sign-matching rules
+SELECT  interval '';  -- error
+ERROR:  invalid input syntax for type interval: ""
+LINE 1: SELECT  interval '';
+                         ^
 -- test outputting iso8601 intervals
 SET IntervalStyle to iso_8601;
 select  interval '0'                                AS "zero",
diff --git a/src/test/regress/sql/interval.sql b/src/test/regress/sql/interval.sql
index 97d33a13236..55a449b6179 100644
--- a/src/test/regress/sql/interval.sql
+++ b/src/test/regress/sql/interval.sql
@@ -277,6 +277,9 @@ SELECT  interval '-23 hours 45 min 12.34 sec',
         interval '-1 year 2 months 1 day 23 hours 45 min 12.34 sec',
         interval '-1 year 2 months 1 day 23 hours 45 min +12.34 sec';
 
+-- edge case for sign-matching rules
+SELECT  interval '';  -- error
+
 -- test outputting iso8601 intervals
 SET IntervalStyle to iso_8601;
 select  interval '0'                                AS "zero",