diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 4298a0dde23..628cc681dc4 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -5613,6 +5613,10 @@ parse_real(const char *value, double *result)
 	if (endptr == value || errno == ERANGE)
 		return false;
 
+	/* reject NaN (infinities will fail range checks later) */
+	if (isnan(val))
+		return false;
+
 	/* allow whitespace after number */
 	while (isspace((unsigned char) *endptr))
 		endptr++;
diff --git a/src/test/regress/expected/guc.out b/src/test/regress/expected/guc.out
index 43ac5f5f11c..4afbd3c4dca 100644
--- a/src/test/regress/expected/guc.out
+++ b/src/test/regress/expected/guc.out
@@ -506,6 +506,11 @@ SELECT '2006-08-13 12:34:56'::timestamptz;
  Sun Aug 13 12:34:56 2006 PDT
 (1 row)
 
+-- Test some simple error cases
+SET seq_page_cost TO 'NaN';
+ERROR:  parameter "seq_page_cost" requires a numeric value
+SET vacuum_cost_delay TO '10s';
+ERROR:  10000 is outside the valid range for parameter "vacuum_cost_delay" (0 .. 100)
 --
 -- Test DISCARD TEMP
 --
diff --git a/src/test/regress/sql/guc.sql b/src/test/regress/sql/guc.sql
index 23e50297800..fa6a9d6c340 100644
--- a/src/test/regress/sql/guc.sql
+++ b/src/test/regress/sql/guc.sql
@@ -144,6 +144,10 @@ RESET datestyle;
 SHOW datestyle;
 SELECT '2006-08-13 12:34:56'::timestamptz;
 
+-- Test some simple error cases
+SET seq_page_cost TO 'NaN';
+SET vacuum_cost_delay TO '10s';
+
 --
 -- Test DISCARD TEMP
 --