diff --git a/builtin/builtin.go b/builtin/builtin.go
index 43b08b78..d76cc9d0 100644
--- a/builtin/builtin.go
+++ b/builtin/builtin.go
@@ -972,33 +972,36 @@ var Builtins = []*ast.Function{
 			return arrayType, nil
 		},
 	},
-	{
-		Name: "bitand",
-		Func: func(args ...any) (any, error) {
-			return bitFunc("bitand", func(x, y int) (any, error) {
-				return x & y, nil
-			}, args)
-		},
-		Types: types(new(func(int, int) int)),
-	},
-	{
-		Name: "bitor",
-		Func: func(args ...any) (any, error) {
-			return bitFunc("bitor", func(x, y int) (any, error) {
-				return x | y, nil
-			}, args)
-		},
-		Types: types(new(func(int, int) int)),
-	},
-	{
-		Name: "bitxor",
-		Func: func(args ...any) (any, error) {
-			return bitFunc("bitxor", func(x, y int) (any, error) {
-				return x ^ y, nil
-			}, args)
-		},
-		Types: types(new(func(int, int) int)),
-	},
+	bitFunc("bitand", func(x, y int) (any, error) {
+		return x & y, nil
+	}),
+	bitFunc("bitor", func(x, y int) (any, error) {
+		return x | y, nil
+	}),
+	bitFunc("bitxor", func(x, y int) (any, error) {
+		return x ^ y, nil
+	}),
+	bitFunc("bitnand", func(x, y int) (any, error) {
+		return x &^ y, nil
+	}),
+	bitFunc("bitshl", func(x, y int) (any, error) {
+		if y < 0 {
+			return nil, fmt.Errorf("invalid operation: negative shift count %d (type int)", y)
+		}
+		return x << y, nil
+	}),
+	bitFunc("bitshr", func(x, y int) (any, error) {
+		if y < 0 {
+			return nil, fmt.Errorf("invalid operation: negative shift count %d (type int)", y)
+		}
+		return x >> y, nil
+	}),
+	bitFunc("bitushr", func(x, y int) (any, error) {
+		if y < 0 {
+			return nil, fmt.Errorf("invalid operation: negative shift count %d (type int)", y)
+		}
+		return int(uint(x) >> y), nil
+	}),
 	{
 		Name: "bitnot",
 		Func: func(args ...any) (any, error) {
@@ -1011,51 +1014,6 @@ var Builtins = []*ast.Function{
 			}
 			return ^x, nil
 		},
-		Types: types(new(func(int) any)),
-	},
-	{
-		Name: "bitnand",
-		Func: func(args ...any) (any, error) {
-			return bitFunc("bitnand", func(x, y int) (any, error) {
-				return x &^ y, nil
-			}, args)
-		},
-		Types: types(new(func(int, int) int)),
-	},
-	{
-		Name: "bitshr",
-		Func: func(args ...any) (any, error) {
-			return bitFunc("bitshr", func(x, y int) (any, error) {
-				if y < 0 {
-					return nil, fmt.Errorf("invalid operation: negative shift count %d (type int)", y)
-				}
-				return x >> y, nil
-			}, args)
-		},
-		Types: types(new(func(int, int) int)),
-	},
-	{
-		Name: "bitshl",
-		Func: func(args ...any) (any, error) {
-			return bitFunc("bitshl", func(x, y int) (any, error) {
-				if y < 0 {
-					return nil, fmt.Errorf("invalid operation: negative shift count %d (type int)", y)
-				}
-				return x << y, nil
-			}, args)
-		},
-		Types: types(new(func(int, int) int)),
-	},
-	{
-		Name: "bitushr",
-		Func: func(args ...any) (any, error) {
-			return bitFunc("bitushr", func(x, y int) (any, error) {
-				if y < 0 {
-					return nil, fmt.Errorf("invalid operation: negative shift count %d (type int)", y)
-				}
-				return int(uint(x) >> y), nil
-			}, args)
-		},
-		Types: types(new(func(int, int) int)),
+		Types: types(new(func(int) int)),
 	},
 }
diff --git a/builtin/func.go b/builtin/func.go
index cd347ba1..1c2546a2 100644
--- a/builtin/func.go
+++ b/builtin/func.go
@@ -6,6 +6,7 @@ import (
 	"reflect"
 	"strconv"
 
+	"github.com/expr-lang/expr/ast"
 	"github.com/expr-lang/expr/vm/runtime"
 )
 
@@ -273,17 +274,23 @@ func Min(args ...any) (any, error) {
 	return min, nil
 }
 
-func bitFunc(name string, fn func(x, y int) (any, error), args []any) (any, error) {
-	if len(args) != 2 {
-		return nil, fmt.Errorf("invalid number of arguments for %s (expected 2, got %d)", name, len(args))
+func bitFunc(name string, fn func(x, y int) (any, error)) *ast.Function {
+	return &ast.Function{
+		Name: name,
+		Func: func(args ...any) (any, error) {
+			if len(args) != 2 {
+				return nil, fmt.Errorf("invalid number of arguments for %s (expected 2, got %d)", name, len(args))
+			}
+			x, err := toInt(args[0])
+			if err != nil {
+				return nil, fmt.Errorf("%v to call %s", err, name)
+			}
+			y, err := toInt(args[1])
+			if err != nil {
+				return nil, fmt.Errorf("%v to call %s", err, name)
+			}
+			return fn(x, y)
+		},
+		Types: types(new(func(int, int) int)),
 	}
-	x, err := toInt(args[0])
-	if err != nil {
-		return nil, fmt.Errorf("%v to call %s", err, name)
-	}
-	y, err := toInt(args[1])
-	if err != nil {
-		return nil, fmt.Errorf("%v to call %s", err, name)
-	}
-	return fn(x, y)
 }