diff --git a/connectors/jdk-connector/src/main/java/org/glassfish/jersey/jdk/connector/internal/HttpRequestEncoder.java b/connectors/jdk-connector/src/main/java/org/glassfish/jersey/jdk/connector/internal/HttpRequestEncoder.java
index d1a116b078..6b04b59742 100644
--- a/connectors/jdk-connector/src/main/java/org/glassfish/jersey/jdk/connector/internal/HttpRequestEncoder.java
+++ b/connectors/jdk-connector/src/main/java/org/glassfish/jersey/jdk/connector/internal/HttpRequestEncoder.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2019 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2021 Oracle and/or its affiliates. All rights reserved.
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License v. 2.0, which is available at
@@ -36,10 +36,11 @@ class HttpRequestEncoder {
 
     private static void appendUpgradeHeaders(StringBuilder request, Map<String, List<String>> headers) {
         for (Map.Entry<String, List<String>> header : headers.entrySet()) {
+            String delimiter = "Cookie".equalsIgnoreCase(header.getKey()) ? "; " : ",";
             StringBuilder value = new StringBuilder();
             for (String valuePart : header.getValue()) {
                 if (value.length() != 0) {
-                    value.append(",");
+                    value.append(delimiter);
                 }
                 value.append(valuePart);
             }
diff --git a/core-client/src/main/java/org/glassfish/jersey/client/internal/HttpUrlConnector.java b/core-client/src/main/java/org/glassfish/jersey/client/internal/HttpUrlConnector.java
index 443c8573ed..568b9cb221 100644
--- a/core-client/src/main/java/org/glassfish/jersey/client/internal/HttpUrlConnector.java
+++ b/core-client/src/main/java/org/glassfish/jersey/client/internal/HttpUrlConnector.java
@@ -425,6 +425,7 @@ private void setOutboundHeaders(MultivaluedMap<String, String> headers, HttpURLC
         boolean restrictedSent = false;
         for (Map.Entry<String, List<String>> header : headers.entrySet()) {
             String headerName = header.getKey();
+            String delimiter = "Cookie".equalsIgnoreCase(headerName) ? "; " : ",";
             String headerValue;
 
             List<String> headerValues = header.getValue();
@@ -436,7 +437,7 @@ private void setOutboundHeaders(MultivaluedMap<String, String> headers, HttpURLC
                 boolean add = false;
                 for (Object value : headerValues) {
                     if (add) {
-                        b.append(',');
+                        b.append(delimiter);
                     }
                     add = true;
                     b.append(value);