diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 344a3188317b..c353001c581c 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -512,7 +512,7 @@ cost_gather_merge(GatherMergePath *path, PlannerInfo *root,
 	logN = LOG2(N);
 
 	/* Assumed cost per tuple comparison */
-	comparison_cost = 2.0 * cpu_operator_cost;
+	comparison_cost = 3.9 * cpu_operator_cost;
 
 	/* Heap creation cost */
 	startup_cost += comparison_cost * N * logN;
@@ -2474,7 +2474,7 @@ cost_merge_append(Path *path, PlannerInfo *root,
 	logN = LOG2(N);
 
 	/* Assumed cost per tuple comparison */
-	comparison_cost = 2.0 * cpu_operator_cost;
+	comparison_cost = 3.9 * cpu_operator_cost;
 
 	/* Heap creation cost */
 	startup_cost += comparison_cost * N * logN;