diff --git a/core/src/main/java/org/dcsa/conformance/core/party/ConformanceParty.java b/core/src/main/java/org/dcsa/conformance/core/party/ConformanceParty.java
index da12baf3..8030c37f 100644
--- a/core/src/main/java/org/dcsa/conformance/core/party/ConformanceParty.java
+++ b/core/src/main/java/org/dcsa/conformance/core/party/ConformanceParty.java
@@ -18,6 +18,7 @@
 import org.dcsa.conformance.core.scenario.ConformanceAction;
 import org.dcsa.conformance.core.state.JsonNodeMap;
 import org.dcsa.conformance.core.state.StatefulEntity;
+import org.dcsa.conformance.core.toolkit.JsonToolkit;
 import org.dcsa.conformance.core.traffic.ConformanceMessage;
 import org.dcsa.conformance.core.traffic.ConformanceMessageBody;
 import org.dcsa.conformance.core.traffic.ConformanceRequest;
@@ -229,12 +230,15 @@ private void _asyncCounterpartPatchPostOrPut(
                 counterpartConfiguration.getName(),
                 counterpartConfiguration.getRole(),
                 counterpartConfiguration.getAuthHeaderName().isBlank()
-                    ? Map.of("Api-Version", List.of(apiVersion))
-                    : Map.of(
-                        "Api-Version",
-                        List.of(apiVersion),
-                        counterpartConfiguration.getAuthHeaderName(),
-                        List.of(counterpartConfiguration.getAuthHeaderValue())),
+                    ? Map.ofEntries(
+                        Map.entry("Api-Version", List.of(apiVersion)),
+                        Map.entry("Content-Type", List.of(JsonToolkit.JSON_UTF_8)))
+                    : Map.ofEntries(
+                        Map.entry("Api-Version", List.of(apiVersion)),
+                        Map.entry("Content-Type", List.of(JsonToolkit.JSON_UTF_8)),
+                        Map.entry(
+                            counterpartConfiguration.getAuthHeaderName(),
+                            List.of(counterpartConfiguration.getAuthHeaderValue()))),
                 new ConformanceMessageBody(jsonBody),
                 System.currentTimeMillis())),
         responseCallback);
diff --git a/core/src/main/java/org/dcsa/conformance/core/toolkit/JsonToolkit.java b/core/src/main/java/org/dcsa/conformance/core/toolkit/JsonToolkit.java
index e854f27f..eb740c02 100644
--- a/core/src/main/java/org/dcsa/conformance/core/toolkit/JsonToolkit.java
+++ b/core/src/main/java/org/dcsa/conformance/core/toolkit/JsonToolkit.java
@@ -15,7 +15,7 @@
 public enum JsonToolkit {
   ; // no instances
 
-  public static final String JSON_UTF_8 = "application/json;charset=utf-8";
+  public static final String JSON_UTF_8 = "application/json";
 
   @SneakyThrows
   public static JsonNode stringToJsonNode(String string) {