diff --git a/src/main/java/com/bunq/sdk/http/ApiClient.java b/src/main/java/com/bunq/sdk/http/ApiClient.java
index eb9321e9..7a50a2e2 100644
--- a/src/main/java/com/bunq/sdk/http/ApiClient.java
+++ b/src/main/java/com/bunq/sdk/http/ApiClient.java
@@ -243,7 +243,7 @@ private void setDefaultHeaders(BunqRequestBuilder httpEntity) {
      */
     private void setCustomHeaders(Request.Builder requestBuilder, Map<String, String> customHeaders) {
         for (Map.Entry<String, String> entry : customHeaders.entrySet()) {
-            requestBuilder.addHeader(entry.getKey(), entry.getValue());
+            requestBuilder.header(entry.getKey(), entry.getValue());
         }
     }