diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 46c95b0..c83135a 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -3414,6 +3414,8 @@ estimate_num_groups(PlannerInfo *root, List *groupExprs, double input_rows,
                Assert(rel->reloptkind == RELOPT_BASEREL);
                if (rel->tuples > 0)
                {
+                       double          old_factor;             /* The way it is currently done on master */
+                       double          new_factor;             /* The way Tomas Vondra proposes doing it */
                        /*
                         * Clamp to size of rel, or size of rel / 10 if multiple Vars. The
                         * fudge factor is because the Vars are probably correlated but we
@@ -3440,7 +3442,10 @@ estimate_num_groups(PlannerInfo *root, List *groupExprs, double input_rows,
                        /*
                         * Multiply by restriction selectivity.
                         */
-                       reldistinct *= rel->rows / rel->tuples;
+                       old_factor = rel->rows / rel->tuples;           /* old way */
+                       new_factor = (1 - powl((reldistinct - 1) / reldistinct, rel->rows));  /* Tomas's way */
+
+                       reldistinct *= sqrt(old_factor * new_factor);   /* average of old way and new way, sort of */
 
                        /*
                         * Update estimate of total distinct groups.