diff --git a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/HttpAsyncClientBuilder.java b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/HttpAsyncClientBuilder.java
index 346d315c8..a3c45dc0f 100644
--- a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/HttpAsyncClientBuilder.java
+++ b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/HttpAsyncClientBuilder.java
@@ -779,7 +779,11 @@ protected void addCloseable(final Closeable closeable) {
     public CloseableHttpAsyncClient build() {
         AsyncClientConnectionManager connManagerCopy = this.connManager;
         if (connManagerCopy == null) {
-            connManagerCopy = PoolingAsyncClientConnectionManagerBuilder.create().build();
+            final PoolingAsyncClientConnectionManagerBuilder connectionManagerBuilder = PoolingAsyncClientConnectionManagerBuilder.create();
+            if (systemProperties) {
+                connectionManagerBuilder.useSystemProperties();
+            }
+            connManagerCopy = connectionManagerBuilder.build();
         }
 
         ConnectionKeepAliveStrategy keepAliveStrategyCopy = this.keepAliveStrategy;
diff --git a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/HttpClientBuilder.java b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/HttpClientBuilder.java
index 8711f4315..c040bf84d 100644
--- a/httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/HttpClientBuilder.java
+++ b/httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/HttpClientBuilder.java
@@ -749,7 +749,11 @@ public CloseableHttpClient build() {
         }
         HttpClientConnectionManager connManagerCopy = this.connManager;
         if (connManagerCopy == null) {
-            connManagerCopy = PoolingHttpClientConnectionManagerBuilder.create().build();
+            final PoolingHttpClientConnectionManagerBuilder connectionManagerBuilder = PoolingHttpClientConnectionManagerBuilder.create();
+            if (systemProperties) {
+                connectionManagerBuilder.useSystemProperties();
+            }
+            connManagerCopy = connectionManagerBuilder.build();
         }
         ConnectionReuseStrategy reuseStrategyCopy = this.reuseStrategy;
         if (reuseStrategyCopy == null) {