diff --git a/openapi.go b/openapi.go
index 44da110..10f8c8b 100644
--- a/openapi.go
+++ b/openapi.go
@@ -721,7 +721,7 @@ func securitySchemeComponents(overrides map[string]any) map[string]any {
 		if name == "" || scheme == nil {
 			continue
 		}
-		schemes[name] = scheme
+		schemes[name] = cloneOpenAPIValue(scheme)
 	}
 
 	return schemes
diff --git a/options.go b/options.go
index 3b99ee2..80952ed 100644
--- a/options.go
+++ b/options.go
@@ -266,7 +266,7 @@ func WithSwaggerSecuritySchemes(schemes map[string]any) Option {
 			if name == "" || scheme == nil {
 				continue
 			}
-			e.swaggerSecuritySchemes[name] = scheme
+			e.swaggerSecuritySchemes[name] = cloneOpenAPIValue(scheme)
 		}
 	}
 }
diff --git a/spec_builder_helper.go b/spec_builder_helper.go
index 463b768..23cd167 100644
--- a/spec_builder_helper.go
+++ b/spec_builder_helper.go
@@ -3,6 +3,7 @@
 package api
 
 import (
+	"reflect"
 	"slices"
 )
 
@@ -52,7 +53,61 @@ func cloneSecuritySchemes(schemes map[string]any) map[string]any {
 
 	out := make(map[string]any, len(schemes))
 	for name, scheme := range schemes {
-		out[name] = scheme
+		out[name] = cloneOpenAPIValue(scheme)
 	}
 	return out
 }
+
+// cloneOpenAPIValue recursively copies JSON-like OpenAPI values so callers can
+// safely retain and reuse their original maps after configuring an engine.
+func cloneOpenAPIValue(v any) any {
+	switch value := v.(type) {
+	case map[string]any:
+		out := make(map[string]any, len(value))
+		for k, nested := range value {
+			out[k] = cloneOpenAPIValue(nested)
+		}
+		return out
+	case []any:
+		out := make([]any, len(value))
+		for i, nested := range value {
+			out[i] = cloneOpenAPIValue(nested)
+		}
+		return out
+	default:
+		rv := reflect.ValueOf(v)
+		if !rv.IsValid() {
+			return nil
+		}
+
+		switch rv.Kind() {
+		case reflect.Map:
+			out := reflect.MakeMapWithSize(rv.Type(), rv.Len())
+			for _, key := range rv.MapKeys() {
+				cloned := cloneOpenAPIValue(rv.MapIndex(key).Interface())
+				if cloned == nil {
+					out.SetMapIndex(key, reflect.Zero(rv.Type().Elem()))
+					continue
+				}
+				out.SetMapIndex(key, reflect.ValueOf(cloned))
+			}
+			return out.Interface()
+		case reflect.Slice:
+			if rv.IsNil() {
+				return v
+			}
+			out := reflect.MakeSlice(rv.Type(), rv.Len(), rv.Len())
+			for i := 0; i < rv.Len(); i++ {
+				cloned := cloneOpenAPIValue(rv.Index(i).Interface())
+				if cloned == nil {
+					out.Index(i).Set(reflect.Zero(rv.Type().Elem()))
+					continue
+				}
+				out.Index(i).Set(reflect.ValueOf(cloned))
+			}
+			return out.Interface()
+		default:
+			return value
+		}
+	}
+}
diff --git a/spec_builder_helper_test.go b/spec_builder_helper_test.go
index e549889..f5f5f9a 100644
--- a/spec_builder_helper_test.go
+++ b/spec_builder_helper_test.go
@@ -312,3 +312,56 @@ func TestEngine_Good_OpenAPISpecBuilderCarriesConfiguredSSEPathWithoutBroker(t *
 		t.Fatalf("expected x-sse-path=/events, got %v", got)
 	}
 }
+
+func TestEngine_Good_OpenAPISpecBuilderClonesSecuritySchemes(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	securityScheme := map[string]any{
+		"type": "oauth2",
+		"flows": map[string]any{
+			"clientCredentials": map[string]any{
+				"tokenUrl": "https://auth.example.com/token",
+			},
+		},
+	}
+	schemes := map[string]any{
+		"oauth2": securityScheme,
+	}
+
+	e, err := api.New(
+		api.WithSwagger("Engine API", "Engine metadata", "2.0.0"),
+		api.WithSwaggerSecuritySchemes(schemes),
+	)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// Mutate the original input after configuration. The builder snapshot should
+	// remain stable and keep the original token URL.
+	securityScheme["type"] = "mutated"
+	securityScheme["flows"].(map[string]any)["clientCredentials"].(map[string]any)["tokenUrl"] = "https://mutated.example.com/token"
+
+	data, err := e.OpenAPISpecBuilder().Build(nil)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	var spec map[string]any
+	if err := json.Unmarshal(data, &spec); err != nil {
+		t.Fatalf("invalid JSON: %v", err)
+	}
+
+	securitySchemes := spec["components"].(map[string]any)["securitySchemes"].(map[string]any)
+	oauth2, ok := securitySchemes["oauth2"].(map[string]any)
+	if !ok {
+		t.Fatal("expected oauth2 security scheme in generated spec")
+	}
+	if oauth2["type"] != "oauth2" {
+		t.Fatalf("expected cloned oauth2.type=oauth2, got %v", oauth2["type"])
+	}
+	flows := oauth2["flows"].(map[string]any)
+	clientCredentials := flows["clientCredentials"].(map[string]any)
+	if clientCredentials["tokenUrl"] != "https://auth.example.com/token" {
+		t.Fatalf("expected original tokenUrl to be preserved, got %v", clientCredentials["tokenUrl"])
+	}
+}