diff --git a/client.go b/client.go
index c436e12..7eabeed 100644
--- a/client.go
+++ b/client.go
@@ -10,6 +10,7 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"reflect"
 	"strings"
 	"sync"
 
@@ -270,7 +271,7 @@ func (c *OpenAPIClient) buildURL(op openAPIOperation, params map[string]any) (st
 	query := url.Values{}
 	if explicitQuery, ok := nestedMap(params, "query"); ok {
 		for key, value := range explicitQuery {
-			query.Set(key, fmt.Sprint(value))
+			appendQueryValue(query, key, value)
 		}
 	}
 	if op.method == http.MethodGet || (op.method == http.MethodHead && !op.hasRequestBody) {
@@ -284,7 +285,7 @@ func (c *OpenAPIClient) buildURL(op openAPIOperation, params map[string]any) (st
 			if _, exists := query[key]; exists {
 				continue
 			}
-			query.Set(key, fmt.Sprint(value))
+			appendQueryValue(query, key, value)
 		}
 	}
 
@@ -413,3 +414,42 @@ func containsString(values []string, target string) bool {
 	}
 	return false
 }
+
+func appendQueryValue(query url.Values, key string, value any) {
+	switch v := value.(type) {
+	case nil:
+		return
+	case []byte:
+		query.Add(key, string(v))
+		return
+	case []string:
+		for _, item := range v {
+			query.Add(key, item)
+		}
+		return
+	case []any:
+		for _, item := range v {
+			appendQueryValue(query, key, item)
+		}
+		return
+	}
+
+	rv := reflect.ValueOf(value)
+	if !rv.IsValid() {
+		return
+	}
+
+	switch rv.Kind() {
+	case reflect.Slice, reflect.Array:
+		if rv.Type().Elem().Kind() == reflect.Uint8 {
+			query.Add(key, string(rv.Bytes()))
+			return
+		}
+		for i := 0; i < rv.Len(); i++ {
+			appendQueryValue(query, key, rv.Index(i).Interface())
+		}
+		return
+	}
+
+	query.Add(key, fmt.Sprint(value))
+}
diff --git a/client_test.go b/client_test.go
index ebe7e12..884f43c 100644
--- a/client_test.go
+++ b/client_test.go
@@ -194,6 +194,69 @@ paths:
 	}
 }
 
+func TestOpenAPIClient_Good_CallOperationWithRepeatedQueryValues(t *testing.T) {
+	errCh := make(chan error, 1)
+	mux := http.NewServeMux()
+	mux.HandleFunc("/search", func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodGet {
+			errCh <- fmt.Errorf("expected GET, got %s", r.Method)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+		if got := r.URL.Query()["tag"]; len(got) != 2 || got[0] != "alpha" || got[1] != "beta" {
+			errCh <- fmt.Errorf("expected repeated tag values [alpha beta], got %v", got)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+		if got := r.URL.Query().Get("page"); got != "2" {
+			errCh <- fmt.Errorf("expected page=2, got %q", got)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"success":true,"data":{"ok":true}}`))
+	})
+
+	srv := httptest.NewServer(mux)
+	defer srv.Close()
+
+	specPath := writeTempSpec(t, `openapi: 3.1.0
+info:
+  title: Test API
+  version: 1.0.0
+paths:
+  /search:
+    get:
+      operationId: search_items
+`)
+
+	client := api.NewOpenAPIClient(
+		api.WithSpec(specPath),
+		api.WithBaseURL(srv.URL),
+	)
+
+	result, err := client.Call("search_items", map[string]any{
+		"tag":  []string{"alpha", "beta"},
+		"page": 2,
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	select {
+	case err := <-errCh:
+		t.Fatal(err)
+	default:
+	}
+
+	decoded, ok := result.(map[string]any)
+	if !ok {
+		t.Fatalf("expected map result, got %T", result)
+	}
+	if okValue, ok := decoded["ok"].(bool); !ok || !okValue {
+		t.Fatalf("expected ok=true, got %#v", decoded["ok"])
+	}
+}
+
 func TestOpenAPIClient_Bad_MissingOperation(t *testing.T) {
 	specPath := writeTempSpec(t, `openapi: 3.1.0
 info: