diff --git a/postgis/geography_measurement.c b/postgis/geography_measurement.c
index 803b437061ba87880a6dd193593e175c2b6bfcde..05776c7202d38365e77a5ef6bb23bdab58d93707 100644
--- a/postgis/geography_measurement.c
+++ b/postgis/geography_measurement.c
@@ -55,7 +55,7 @@ Datum geography_segmentize(PG_FUNCTION_ARGS);
 PG_FUNCTION_INFO_V1(geography_distance_knn);
 Datum geography_distance_knn(PG_FUNCTION_ARGS)
 {
-	return DirectFunctionCall3(geography_distance_uncached, 
+	return DirectFunctionCall4(geography_distance_uncached, 
 		PG_GETARG_DATUM(0), 
 		PG_GETARG_DATUM(1), 
 		(Datum)0,