# UNDF: UNDF-2026-000000071
--- a/app.go
+++ b/app.go
@@ -98,6 +98,8 @@ type App struct {
 	// ...existing fields...
 	customBinders []CustomBinder
+	customBindersByMIME map[string]CustomBinder
+	customBindersByName map[string]CustomBinder
 	// ...
 }

@@ -549,6 +551,8 @@ func New(config ...Config) *App {
 	app := &App{
 		// ...existing...
 		customBinders: []CustomBinder{},
+		customBindersByMIME: make(map[string]CustomBinder),
+		customBindersByName: make(map[string]CustomBinder),
 	}
 	// ...
 }

@@ -733,6 +735,9 @@ func (app *App) RegisterCustomBinder(customBinder CustomBinder) {
 	app.customBinders = append(app.customBinders, customBinder)
+	for _, mime := range customBinder.MIMETypes() {
+		app.customBindersByMIME[mime] = customBinder
+	}
+	app.customBindersByName[customBinder.Name()] = customBinder
 }

--- a/bind.go
+++ b/bind.go
@@ -389,12 +389,10 @@ func (b *Bind) Body(out any) error {
 	ctype = binder.FilterFlags(utils.ParseVendorSpecificContentType(ctype))

 	// Check custom binders — O(1) map lookup instead of O(B×M) nested scan
-	binders := b.ctx.App().customBinders
-	for _, customBinder := range binders {
-		if slices.Contains(customBinder.MIMETypes(), ctype) {
-			if err := b.returnBindErr(customBinder.Parse(b.ctx, out), BindSourceBody); err != nil {
-				return err
-			}
-			return b.validateStruct(out)
+	if customBinder, ok := b.ctx.App().customBindersByMIME[ctype]; ok {
+		if err := b.returnBindErr(customBinder.Parse(b.ctx, out), BindSourceBody); err != nil {
+			return err
 		}
+		return b.validateStruct(out)
 	}

@@ -213,10 +213,8 @@ func (b *Bind) Custom(name string, dest any) error {
-	binders := b.ctx.App().customBinders
-	for _, customBinder := range binders {
-		if customBinder.Name() == name {
-			if err := b.returnBindErr(customBinder.Parse(b.ctx, dest), name); err != nil {
-				return err
-			}
-			return b.validateStruct(dest)
-		}
+	if customBinder, ok := b.ctx.App().customBindersByName[name]; ok {
+		if err := b.returnBindErr(customBinder.Parse(b.ctx, dest), name); err != nil {
+			return err
 	}
+		return b.validateStruct(dest)
+	}

 	return ErrCustomBinderNotFound
 }