diff --git a/solr/CHANGES.txt b/solr/CHANGES.txt
index b36bf6135eb..fd71c1c026c 100644
--- a/solr/CHANGES.txt
+++ b/solr/CHANGES.txt
@@ -99,6 +99,8 @@ Optimizations
   produced. This resulted in up to 3x throughput when small filter creation was the bottleneck,
   as well as orders of magnitude less garbage. (Jeff Wartes, yonik)
 
+* SOLR-8937: bin/post (SimplePostTool) now streams the standard input instead of buffering fully.
+  (David Smiley)
 
 Other Changes
 ----------------------
diff --git a/solr/core/src/java/org/apache/solr/util/SimplePostTool.java b/solr/core/src/java/org/apache/solr/util/SimplePostTool.java
index 448897a1388..44a35ca1987 100644
--- a/solr/core/src/java/org/apache/solr/util/SimplePostTool.java
+++ b/solr/core/src/java/org/apache/solr/util/SimplePostTool.java
@@ -890,7 +890,11 @@ public class SimplePostTool {
           String encoding = DatatypeConverter.printBase64Binary(url.getUserInfo().getBytes(StandardCharsets.US_ASCII));
           urlc.setRequestProperty("Authorization", "Basic " + encoding);
         }
-        if (null != length) urlc.setFixedLengthStreamingMode(length);
+        if (null != length) {
+          urlc.setFixedLengthStreamingMode(length);
+        } else {
+          urlc.setChunkedStreamingMode(-1);//use JDK default chunkLen, 4k in Java 8.
+        }
         urlc.connect();
       } catch (IOException e) {
         fatal("Connection error (is Solr running at " + solrUrl + " ?): " + e);