diff --git a/client.go b/client.go
index 47564d3..3bdc5c1 100644
--- a/client.go
+++ b/client.go
@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"net/url"
 	"path"
+	"sync"
 )
 
 var (
@@ -44,16 +45,15 @@ func NewClient(rawURL, schema string, headers map[string]string) *Client {
 	}
 
 	// Set required headers
-	c.Transport.header.Set("Accept", "application/json")
-	c.Transport.header.Set("Content-Type", "application/json")
-	c.Transport.header.Set("Accept-Profile", schema)
-	c.Transport.header.Set("Content-Profile", schema)
-	c.Transport.header.Set("X-Client-Info", "postgrest-go/"+version)
-
+	c.Transport.SetHeaders(map[string]string{
+		"Accept":          "application/json",
+		"Content-Type":    "application/json",
+		"Accept-Profile":  schema,
+		"Content-Profile": schema,
+		"X-Client-Info":   "postgrest-go/" + version,
+	})
 	// Set optional headers if they exist
-	for key, value := range headers {
-		c.Transport.header.Set(key, value)
-	}
+	c.Transport.SetHeaders(headers)
 
 	return &c
 }
@@ -84,20 +84,22 @@ func (c *Client) Ping() bool {
 
 // SetApiKey sets api key header for subsequent requests.
 func (c *Client) SetApiKey(apiKey string) *Client {
-	c.Transport.header.Set("apikey", apiKey)
+	c.Transport.SetHeader("apikey", apiKey)
 	return c
 }
 
 // SetAuthToken sets authorization header for subsequent requests.
 func (c *Client) SetAuthToken(authToken string) *Client {
-	c.Transport.header.Set("Authorization", "Bearer "+authToken)
+	c.Transport.SetHeader("Authorization", "Bearer "+authToken)
 	return c
 }
 
 // ChangeSchema modifies the schema for subsequent requests.
 func (c *Client) ChangeSchema(schema string) *Client {
-	c.Transport.header.Set("Accept-Profile", schema)
-	c.Transport.header.Set("Content-Profile", schema)
+	c.Transport.SetHeaders(map[string]string{
+		"Accept-Profile":  schema,
+		"Content-Profile": schema,
+	})
 	return c
 }
 
@@ -156,17 +158,35 @@ func (c *Client) Rpc(name string, count string, rpcBody interface{}) string {
 }
 
 type transport struct {
-	header  http.Header
 	baseURL url.URL
 	Parent  http.RoundTripper
+
+	mu     sync.RWMutex
+	header http.Header
+}
+
+func (t *transport) SetHeader(key, value string) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	t.header.Set(key, value)
+}
+
+func (t *transport) SetHeaders(headers map[string]string) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	for key, value := range headers {
+		t.header.Set(key, value)
+	}
 }
 
-func (t transport) RoundTrip(req *http.Request) (*http.Response, error) {
+func (t *transport) RoundTrip(req *http.Request) (*http.Response, error) {
+	t.mu.RLock()
 	for headerName, values := range t.header {
 		for _, val := range values {
 			req.Header.Add(headerName, val)
 		}
 	}
+	t.mu.RUnlock()
 
 	req.URL = t.baseURL.ResolveReference(req.URL)