diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 8fb483a..7ea8688 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -421,7 +421,9 @@ cost_index(IndexPath *path, PlannerInfo *root, double loop_count)
 	 * the fraction of main-table tuples we will have to retrieve) and its
 	 * correlation to the main-table tuple order.
 	 */
-	amcostestimate = index->amcostestimate;		/* cast to proper type */
+
+	/* cast to proper type */
+	amcostestimate = (amcostestimate_function) index->amcostestimate;
 	amcostestimate(root, path, loop_count,
 				   &indexStartupCost, &indexTotalCost,
 				   &indexSelectivity, &indexCorrelation);