@@ -193,11 +193,7 @@ else if (field.equals(ACCEPT_ENCODING)) {
 
     byte[] body = request.body();
 
-    if (body != null && (body.length > 0 || request.httpMethod() != Request.HttpMethod.GET)) {
-      /*
-       * Ignore disableRequestBuffering flag if the empty body was set, to ensure that internal
-       * retry logic applies to such requests.
-       */
+    if (body != null && body.length > 0) {
       if (disableRequestBuffering) {
         if (contentLength != null) {
           connection.setFixedLengthStreamingMode(contentLength);
@@ -220,10 +216,15 @@ else if (field.equals(ACCEPT_ENCODING)) {
         } catch (IOException suppressed) { // NOPMD
         }
       }
-    }
-
-    if (body == null && request.httpMethod().isWithBody()) {
-      // To use this Header, set 'sun.net.http.allowRestrictedHeaders' property true.
+    } else if (request.httpMethod().isWithBody()) {
+      /*
+       * Avoid calling connection.getOutputStream() for an empty body: HttpURLConnection defaults
+       * the Content-Type to application/x-www-form-urlencoded as soon as an output stream (a
+       * "poster") is created, even when zero bytes are written to it. Setting Content-Length
+       * directly ensures internal retry logic still applies to such requests, without triggering
+       * that default.
+       * To use this Header, set 'sun.net.http.allowRestrictedHeaders' property true.
+       */
       connection.addRequestProperty("Content-Length", "0");
     }
 
 
@@ -229,6 +229,16 @@ public void noResponseBodyForPut() throws Exception {
     api.noPutBody();
   }
 
+  @Test
+  void emptyStringBodyForPost() throws Exception {
+    server.enqueue(new MockResponse());
+
+    TestInterface api =
+        newBuilder().target(TestInterface.class, "http://localhost:" + server.getPort());
+
+    api.postEmptyStringBody("");
+  }
+
   /**
    * Some client implementation tests should override this test if the PATCH operation is
    * unsupported.
@@ -612,6 +622,9 @@ public interface TestInterface {
     @RequestLine("POST")
     String noPostBody();
 
+    @RequestLine("POST /")
+    String postEmptyStringBody(String body);
+
     @RequestLine("PUT")
     String noPutBody();
 
 
@@ -165,6 +165,15 @@ void emptyBodyDoesNotConvertGetToPost() throws Exception {
     MockWebServerAssertions.assertThat(server.takeRequest()).hasMethod("GET");
   }
 
+  @Test
+  @Override
+  void emptyStringBodyForPost() throws Exception {
+    super.emptyStringBodyForPost();
+    MockWebServerAssertions.assertThat(server.takeRequest())
+        .hasMethod("POST")
+        .hasNoHeaderNamed("Content-Type");
+  }
+
   @Test
   @Override
   public void noResponseBodyForPut() throws Exception {