diff --git a/expected/epochprop.out b/expected/epochprop.out
index 74e4253..1111f1a 100644
--- a/expected/epochprop.out
+++ b/expected/epochprop.out
@@ -30,7 +30,7 @@ FROM (
                -100) AS tp) AS q;
      to_char     |     to_char     | to_char  | to_char  |  to_char   | to_char  
 -----------------+-----------------+----------+----------+------------+----------
-  269.4744079540 |    4.4055337210 |     .000 | -801.210 |  10361.762 | -###.###
+  269.4744079540 |    4.4055337210 |     .000 | -801.210 |  10361.762 | -110.000
 (1 row)
 
 SELECT
diff --git a/src/epochprop.c b/src/epochprop.c
index 37aab5d..12ad621 100644
--- a/src/epochprop.c
+++ b/src/epochprop.c
@@ -177,11 +177,11 @@ epoch_prop(PG_FUNCTION_ARGS) {
 
 	propagate_phasevec(&input, delta_t, &output);
 
-	/* If we have a null parallax but a good RV, preserve the original,
+	/* If we have an invalid parallax but a good RV, preserve the original,
 		untransformed RV on output.  See
 		https://github.com/ivoa-std/udf-catalogue/pull/20#issuecomment-2115053757
 		for the rationale. */
-	if (!PG_ARGISNULL(4) && PG_ARGISNULL(1)) {
+	if (!PG_ARGISNULL(4) && !input.parallax_valid) {
 		output_null[5] = 0;
 		output.rv = input.rv;
 	}