diff --git a/httpcore5-h2/src/main/java/org/apache/hc/core5/http2/protocol/H2ResponseConformance.java b/httpcore5-h2/src/main/java/org/apache/hc/core5/http2/protocol/H2ResponseConformance.java
index 61e9dc3bb4..a05a6c5fcb 100644
--- a/httpcore5-h2/src/main/java/org/apache/hc/core5/http2/protocol/H2ResponseConformance.java
+++ b/httpcore5-h2/src/main/java/org/apache/hc/core5/http2/protocol/H2ResponseConformance.java
@@ -65,6 +65,7 @@ public H2ResponseConformance() {
         this(
                 HttpHeaders.CONNECTION,
                 HttpHeaders.KEEP_ALIVE,
+                HttpHeaders.PROXY_CONNECTION,
                 HttpHeaders.TRANSFER_ENCODING,
                 HttpHeaders.UPGRADE);
     }
diff --git a/httpcore5-h2/src/test/java/org/apache/hc/core5/http2/protocol/TestH2Interceptors.java b/httpcore5-h2/src/test/java/org/apache/hc/core5/http2/protocol/TestH2Interceptors.java
index 38410c7871..ed3e9365fe 100644
--- a/httpcore5-h2/src/test/java/org/apache/hc/core5/http2/protocol/TestH2Interceptors.java
+++ b/httpcore5-h2/src/test/java/org/apache/hc/core5/http2/protocol/TestH2Interceptors.java
@@ -258,4 +258,20 @@ void testH2ResponseConformanceUpgradeHeader() {
                 "Header 'upgrade: example/1, foo/2' is illegal for HTTP/2 messages");
     }
 
+    @Test
+    void testProxyConnectionRejected() {
+        final BasicHttpResponse response = new BasicHttpResponse(200, "OK");
+        response.addHeader(HttpHeaders.PROXY_CONNECTION, "keep-alive");
+
+        Assertions.assertThrows(
+                ProtocolException.class,
+                () -> H2ResponseConformance.INSTANCE.process(response, null, HttpCoreContext.create()));
+    }
+
+    @Test
+    void testNoIllegalHeaders() throws Exception {
+        final BasicHttpResponse response = new BasicHttpResponse(200, "OK");
+        H2ResponseConformance.INSTANCE.process(response, null, HttpCoreContext.create());
+    }
+
 }