diff --git a/httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/CachedHttpResponseGenerator.java b/httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/CachedHttpResponseGenerator.java
index ff766136a..c827fdad0 100644
--- a/httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/CachedHttpResponseGenerator.java
+++ b/httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/CachedHttpResponseGenerator.java
@@ -139,6 +139,18 @@ class CachedHttpResponseGenerator {
             response.addHeader(varyHeader);
         }
 
+        //Since the goal of a 304 response is to minimize information transfer
+        //when the recipient already has one or more cached representations, a
+        //sender SHOULD NOT generate representation metadata other than the
+        //above listed fields unless said metadata exists for the purpose of
+        //guiding cache updates (e.g., Last-Modified might be useful if the
+        //response does not have an ETag field).
+        if (etagHeader == null) {
+            final Header lastModifiedHeader = entry.getFirstHeader(HttpHeaders.LAST_MODIFIED);
+            if (lastModifiedHeader != null) {
+                response.addHeader(lastModifiedHeader);
+            }
+        }
         return response;
     }
 
diff --git a/httpclient5-cache/src/test/java/org/apache/hc/client5/http/impl/cache/TestCachingExecChain.java b/httpclient5-cache/src/test/java/org/apache/hc/client5/http/impl/cache/TestCachingExecChain.java
index 7f1d3801c..d8bba3720 100644
--- a/httpclient5-cache/src/test/java/org/apache/hc/client5/http/impl/cache/TestCachingExecChain.java
+++ b/httpclient5-cache/src/test/java/org/apache/hc/client5/http/impl/cache/TestCachingExecChain.java
@@ -391,6 +391,7 @@ public class TestCachingExecChain {
         resp1.setHeader("Date", DateUtils.formatStandardDate(now));
         resp1.setHeader("Cache-control", "max-age=600");
         resp1.setHeader("Expires", DateUtils.formatStandardDate(inTenMinutes));
+        resp1.setHeader("ETag", "\"etag\"");
 
         Mockito.when(mockExecChain.proceed(Mockito.any(), Mockito.any())).thenReturn(resp1);
 
@@ -403,6 +404,32 @@ public class TestCachingExecChain {
         Mockito.verify(mockExecChain).proceed(Mockito.any(), Mockito.any());
     }
 
+    @Test
+    public void testReturns304ForIfModifiedSinceHeaderIf304ResponseInCacheWithLastModified() throws Exception {
+        final Instant now = Instant.now();
+        final Instant oneHourAgo = now.minus(1, ChronoUnit.HOURS);
+        final Instant inTenMinutes = now.plus(10, ChronoUnit.MINUTES);
+        final ClassicHttpRequest req1 = new HttpGet("http://foo.example.com/");
+        req1.addHeader("If-Modified-Since", DateUtils.formatStandardDate(oneHourAgo));
+        final ClassicHttpRequest req2 = new HttpGet("http://foo.example.com/");
+        req2.addHeader("If-Modified-Since", DateUtils.formatStandardDate(oneHourAgo));
+
+        final ClassicHttpResponse resp1 = HttpTestUtils.make304Response();
+        resp1.setHeader("Date", DateUtils.formatStandardDate(now));
+        resp1.setHeader("Cache-control", "max-age=600");
+        resp1.setHeader("Expires", DateUtils.formatStandardDate(inTenMinutes));
+
+        Mockito.when(mockExecChain.proceed(Mockito.any(), Mockito.any())).thenReturn(resp1);
+
+        execute(req1);
+
+        final ClassicHttpResponse result = execute(req2);
+        Assertions.assertEquals(HttpStatus.SC_NOT_MODIFIED, result.getCode());
+        Assertions.assertTrue(result.containsHeader("Last-Modified"));
+
+        Mockito.verify(mockExecChain).proceed(Mockito.any(), Mockito.any());
+    }
+
     @Test
     public void testReturns200ForIfModifiedSinceDateIsLess() throws Exception {
         final Instant now = Instant.now();
diff --git a/httpclient5-cache/src/test/java/org/apache/hc/client5/http/impl/cache/TestProtocolRecommendations.java b/httpclient5-cache/src/test/java/org/apache/hc/client5/http/impl/cache/TestProtocolRecommendations.java
index a12de54e4..c1507bb65 100644
--- a/httpclient5-cache/src/test/java/org/apache/hc/client5/http/impl/cache/TestProtocolRecommendations.java
+++ b/httpclient5-cache/src/test/java/org/apache/hc/client5/http/impl/cache/TestProtocolRecommendations.java
@@ -175,6 +175,7 @@ public class TestProtocolRecommendations {
         resp1.setHeader("Cache-Control","max-age=3600");
         resp1.setHeader(validatorHeader, validator);
         resp1.setHeader(headerName, headerValue);
+        resp1.setHeader("ETag", "\"etag\"");
 
         Mockito.when(mockExecChain.proceed(Mockito.any(), Mockito.any())).thenReturn(resp1);