diff --git a/compiler/ast/builtin.go b/compiler/ast/builtin.go
index 38284f5d..4ac1a557 100644
--- a/compiler/ast/builtin.go
+++ b/compiler/ast/builtin.go
@@ -17,9 +17,8 @@ import (
 	"github.com/markkurossi/mpc/types"
 )
 
-// Builtin implements MPCL builtin elements.
+// Builtin implements MPCL builtin functions.
 type Builtin struct {
-	Name string
 	SSA  SSA
 	Eval Eval
 }
@@ -33,27 +32,22 @@ type Eval func(args []AST, env *Env, ctx *Codegen, gen *ssa.Generator,
 	loc utils.Point) (ssa.Value, bool, error)
 
 // Predeclared identifiers.
-var builtins = []Builtin{
-	{
-		Name: "copy",
-		SSA:  copySSA,
+var builtins = map[string]Builtin{
+	"copy": {
+		SSA: copySSA,
 	},
-	{
-		Name: "floorPow2",
+	"floorPow2": {
 		SSA:  floorPow2SSA,
 		Eval: floorPow2Eval,
 	},
-	{
-		Name: "len",
+	"len": {
 		SSA:  lenSSA,
 		Eval: lenEval,
 	},
-	{
-		Name: "native",
-		SSA:  nativeSSA,
+	"native": {
+		SSA: nativeSSA,
 	},
-	{
-		Name: "size",
+	"size": {
 		SSA:  sizeSSA,
 		Eval: sizeEval,
 	},
diff --git a/compiler/ast/eval.go b/compiler/ast/eval.go
index 26faf55a..82291492 100644
--- a/compiler/ast/eval.go
+++ b/compiler/ast/eval.go
@@ -133,13 +133,8 @@ func (ast *Call) Eval(env *Env, ctx *Codegen, gen *ssa.Generator) (
 		return ssa.Undefined, false, nil
 	}
 	// Check builtin functions.
-	for _, bi := range builtins {
-		if bi.Name != ast.Ref.Name.Name {
-			continue
-		}
-		if bi.Eval == nil {
-			return ssa.Undefined, false, nil
-		}
+	bi, ok := builtins[ast.Ref.Name.Name]
+	if ok && bi.Eval != nil {
 		return bi.Eval(ast.Exprs, env, ctx, gen, ast.Location())
 	}
 
diff --git a/compiler/ast/ssagen.go b/compiler/ast/ssagen.go
index 998ca917..b3eeecf1 100644
--- a/compiler/ast/ssagen.go
+++ b/compiler/ast/ssagen.go
@@ -636,10 +636,8 @@ func (ast *Call) SSA(block *ssa.Block, ctx *Codegen, gen *ssa.Generator) (
 	}
 	if called == nil {
 		// Check builtin functions.
-		for _, bi := range builtins {
-			if bi.Name != ast.Ref.Name.Name {
-				continue
-			}
+		bi, ok := builtins[ast.Ref.Name.Name]
+		if ok {
 			// Flatten arguments.
 			var args []ssa.Value
 			for _, arg := range callValues {