diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index f4446169f5..58755151fa 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -4648,6 +4648,9 @@ inline_function(Oid funcid, Oid result_type, Oid result_collid,
 	Query	   *querytree;
 	Node	   *newexpr;
 	int		   *usecounts;
+	double	   *paramcosts;
+	Cost		total_param_cost;
+	double		func_cost;
 	ListCell   *arg;
 	int			i;
 
@@ -4839,9 +4842,20 @@ inline_function(Oid funcid, Oid result_type, Oid result_collid,
 	 * substituted.
 	 */
 	usecounts = (int *) palloc0(funcform->pronargs * sizeof(int));
+	paramcosts = (double *) palloc0(funcform->pronargs * sizeof(double));
 	newexpr = substitute_actual_parameters(newexpr, funcform->pronargs,
 										   args, usecounts);
 
+	/*
+	 * Get the cost of the function without parameters.
+	 *
+	 * Calculation based on how costsize.c performs lookup for function costs
+	 * via 'cost_qual_eval_walker'.
+	 */
+	func_cost = get_func_cost(funcid) * cpu_operator_cost;
+
+	total_param_cost = 0.0;
+
 	/* Now check for parameter usage */
 	i = 0;
 	foreach(arg, args)
@@ -4867,10 +4881,10 @@ inline_function(Oid funcid, Oid result_type, Oid result_collid,
 			 */
 			if (contain_subplans(param))
 				goto fail;
+
 			cost_qual_eval(&eval_cost, list_make1(param), NULL);
-			if (eval_cost.startup + eval_cost.per_tuple >
-				10 * cpu_operator_cost)
-				goto fail;
+			paramcosts[i] = (eval_cost.startup + eval_cost.per_tuple);
+			total_param_cost += (eval_cost.startup + eval_cost.per_tuple);
 
 			/*
 			 * Check volatility last since this is more expensive than the
@@ -4883,6 +4897,19 @@ inline_function(Oid funcid, Oid result_type, Oid result_collid,
 	}
 
 	/*
+	 * If the cost of the function is greater than the sum of all the param
+	 * costs, then inline. Otherwise, check the cost of each param.
+	 */
+	if (func_cost * INLINE_FUNC_COST_FACTOR < total_param_cost)
+	{
+		for (i = 0; i < funcform->pronargs; i++)
+		{
+			if (paramcosts[i] > 10 * cpu_operator_cost)
+				goto fail;
+		}
+	}
+
+	/*
 	 * Whew --- we can make the substitution.  Copy the modified expression
 	 * out of the temporary memory context, and clean up.
 	 */
diff --git a/src/include/optimizer/clauses.h b/src/include/optimizer/clauses.h
index ed854fdd40..475df16b28 100644
--- a/src/include/optimizer/clauses.h
+++ b/src/include/optimizer/clauses.h
@@ -20,6 +20,8 @@
 #define is_opclause(clause)		((clause) != NULL && IsA(clause, OpExpr))
 #define is_funcclause(clause)	((clause) != NULL && IsA(clause, FuncExpr))
 
+#define INLINE_FUNC_COST_FACTOR 1
+
 typedef struct
 {
 	int			numWindowFuncs; /* total number of WindowFuncs found */