diff --git a/src/backend/utils/adt/float.c b/src/backend/utils/adt/float.c
index 50ec3d3dde5..ffd1ce8c761 100644
--- a/src/backend/utils/adt/float.c
+++ b/src/backend/utils/adt/float.c
@@ -1088,18 +1088,25 @@ in_range_float8_float8(PG_FUNCTION_ARGS)
 	}
 
 	/*
-	 * Deal with infinite offset (necessarily +inf, at this point).  We must
-	 * special-case this because if base happens to be -inf, their sum would
-	 * be NaN, which is an overflow-ish condition we should avoid.
+	 * Deal with cases where both base and offset are infinite, and computing
+	 * base +/- offset would produce NaN.  This corresponds to a window frame
+	 * whose boundary infinitely precedes +inf or infinitely follows -inf,
+	 * which is not well-defined.  For consistency with other cases involving
+	 * infinities, such as the fact that +inf infinitely follows +inf, we
+	 * choose to assume that +inf infinitely precedes +inf and -inf infinitely
+	 * follows -inf, and therefore that all finite and infinite values are in
+	 * such a window frame.
+	 *
+	 * offset is known positive, so we need only check the sign of base in
+	 * this test.
 	 */
-	if (isinf(offset))
-	{
-		PG_RETURN_BOOL(sub ? !less : less);
-	}
+	if (isinf(offset) && isinf(base) &&
+		(sub ? base > 0 : base < 0))
+		PG_RETURN_BOOL(true);
 
 	/*
 	 * Otherwise it should be safe to compute base +/- offset.  We trust the
-	 * FPU to cope if base is +/-inf or the true sum would overflow, and
+	 * FPU to cope if an input is +/-inf or the true sum would overflow, and
 	 * produce a suitably signed infinity, which will compare properly against
 	 * val whether or not that's infinity.
 	 */
@@ -1157,18 +1164,25 @@ in_range_float4_float8(PG_FUNCTION_ARGS)
 	}
 
 	/*
-	 * Deal with infinite offset (necessarily +inf, at this point).  We must
-	 * special-case this because if base happens to be -inf, their sum would
-	 * be NaN, which is an overflow-ish condition we should avoid.
+	 * Deal with cases where both base and offset are infinite, and computing
+	 * base +/- offset would produce NaN.  This corresponds to a window frame
+	 * whose boundary infinitely precedes +inf or infinitely follows -inf,
+	 * which is not well-defined.  For consistency with other cases involving
+	 * infinities, such as the fact that +inf infinitely follows +inf, we
+	 * choose to assume that +inf infinitely precedes +inf and -inf infinitely
+	 * follows -inf, and therefore that all finite and infinite values are in
+	 * such a window frame.
+	 *
+	 * offset is known positive, so we need only check the sign of base in
+	 * this test.
 	 */
-	if (isinf(offset))
-	{
-		PG_RETURN_BOOL(sub ? !less : less);
-	}
+	if (isinf(offset) && isinf(base) &&
+		(sub ? base > 0 : base < 0))
+		PG_RETURN_BOOL(true);
 
 	/*
 	 * Otherwise it should be safe to compute base +/- offset.  We trust the
-	 * FPU to cope if base is +/-inf or the true sum would overflow, and
+	 * FPU to cope if an input is +/-inf or the true sum would overflow, and
 	 * produce a suitably signed infinity, which will compare properly against
 	 * val whether or not that's infinity.
 	 */
diff --git a/src/test/regress/expected/window.out b/src/test/regress/expected/window.out
index d5fd4045f9f..432edfa0630 100644
--- a/src/test/regress/expected/window.out
+++ b/src/test/regress/expected/window.out
@@ -1936,6 +1936,42 @@ window w as (order by f_float4 range between
   9 |       NaN |           9 |          9
 (10 rows)
 
+select id, f_float4, first_value(id) over w, last_value(id) over w
+from numerics
+window w as (order by f_float4 range between
+             'inf' preceding and 'inf' preceding);
+ id | f_float4  | first_value | last_value 
+----+-----------+-------------+------------
+  0 | -Infinity |           0 |          0
+  1 |        -3 |           0 |          0
+  2 |        -1 |           0 |          0
+  3 |         0 |           0 |          0
+  4 |       1.1 |           0 |          0
+  5 |      1.12 |           0 |          0
+  6 |         2 |           0 |          0
+  7 |       100 |           0 |          0
+  8 |  Infinity |           0 |          8
+  9 |       NaN |           9 |          9
+(10 rows)
+
+select id, f_float4, first_value(id) over w, last_value(id) over w
+from numerics
+window w as (order by f_float4 range between
+             'inf' following and 'inf' following);
+ id | f_float4  | first_value | last_value 
+----+-----------+-------------+------------
+  0 | -Infinity |           0 |          8
+  1 |        -3 |           8 |          8
+  2 |        -1 |           8 |          8
+  3 |         0 |           8 |          8
+  4 |       1.1 |           8 |          8
+  5 |      1.12 |           8 |          8
+  6 |         2 |           8 |          8
+  7 |       100 |           8 |          8
+  8 |  Infinity |           8 |          8
+  9 |       NaN |           9 |          9
+(10 rows)
+
 select id, f_float4, first_value(id) over w, last_value(id) over w
 from numerics
 window w as (order by f_float4 range between
@@ -1995,6 +2031,42 @@ window w as (order by f_float8 range between
   9 |       NaN |           9 |          9
 (10 rows)
 
+select id, f_float8, first_value(id) over w, last_value(id) over w
+from numerics
+window w as (order by f_float8 range between
+             'inf' preceding and 'inf' preceding);
+ id | f_float8  | first_value | last_value 
+----+-----------+-------------+------------
+  0 | -Infinity |           0 |          0
+  1 |        -3 |           0 |          0
+  2 |        -1 |           0 |          0
+  3 |         0 |           0 |          0
+  4 |       1.1 |           0 |          0
+  5 |      1.12 |           0 |          0
+  6 |         2 |           0 |          0
+  7 |       100 |           0 |          0
+  8 |  Infinity |           0 |          8
+  9 |       NaN |           9 |          9
+(10 rows)
+
+select id, f_float8, first_value(id) over w, last_value(id) over w
+from numerics
+window w as (order by f_float8 range between
+             'inf' following and 'inf' following);
+ id | f_float8  | first_value | last_value 
+----+-----------+-------------+------------
+  0 | -Infinity |           0 |          8
+  1 |        -3 |           8 |          8
+  2 |        -1 |           8 |          8
+  3 |         0 |           8 |          8
+  4 |       1.1 |           8 |          8
+  5 |      1.12 |           8 |          8
+  6 |         2 |           8 |          8
+  7 |       100 |           8 |          8
+  8 |  Infinity |           8 |          8
+  9 |       NaN |           9 |          9
+(10 rows)
+
 select id, f_float8, first_value(id) over w, last_value(id) over w
 from numerics
 window w as (order by f_float8 range between
diff --git a/src/test/regress/sql/window.sql b/src/test/regress/sql/window.sql
index fe273aa31e6..51ec0bac9ad 100644
--- a/src/test/regress/sql/window.sql
+++ b/src/test/regress/sql/window.sql
@@ -524,6 +524,14 @@ window w as (order by f_float4 range between
              'inf' preceding and 'inf' following);
 select id, f_float4, first_value(id) over w, last_value(id) over w
 from numerics
+window w as (order by f_float4 range between
+             'inf' preceding and 'inf' preceding);
+select id, f_float4, first_value(id) over w, last_value(id) over w
+from numerics
+window w as (order by f_float4 range between
+             'inf' following and 'inf' following);
+select id, f_float4, first_value(id) over w, last_value(id) over w
+from numerics
 window w as (order by f_float4 range between
              1.1 preceding and 'NaN' following);  -- error, NaN disallowed
 
@@ -541,6 +549,14 @@ window w as (order by f_float8 range between
              'inf' preceding and 'inf' following);
 select id, f_float8, first_value(id) over w, last_value(id) over w
 from numerics
+window w as (order by f_float8 range between
+             'inf' preceding and 'inf' preceding);
+select id, f_float8, first_value(id) over w, last_value(id) over w
+from numerics
+window w as (order by f_float8 range between
+             'inf' following and 'inf' following);
+select id, f_float8, first_value(id) over w, last_value(id) over w
+from numerics
 window w as (order by f_float8 range between
              1.1 preceding and 'NaN' following);  -- error, NaN disallowed