diff --git a/CHANGES.txt b/CHANGES.txt
index d7a7a61e19..ef6b848ff2 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -3,6 +3,7 @@
  * Fixed multiple single-node SAI query bugs relating to static columns (CASSANDRA-20338)
  * Upgrade com.datastax.cassandra:cassandra-driver-core:3.11.5 to org.apache.cassandra:cassandra-driver-core:3.12.1 (CASSANDRA-17231)
 Merged from 4.0:
+ * Avoid computing prepared statement size for unprepared batches (CASSANDRA-20556)
  * Fix Dropwizard Meter causes timeouts when infrequently used (CASSANDRA-19332)
 
 
diff --git a/src/java/org/apache/cassandra/cql3/QueryProcessor.java b/src/java/org/apache/cassandra/cql3/QueryProcessor.java
index feea4187e4..4547a8fabd 100644
--- a/src/java/org/apache/cassandra/cql3/QueryProcessor.java
+++ b/src/java/org/apache/cassandra/cql3/QueryProcessor.java
@@ -417,6 +417,11 @@ public class QueryProcessor implements QueryHandler
     }
 
     public static Prepared parseAndPrepare(String query, ClientState clientState, boolean isInternal) throws RequestValidationException
+    {
+        return parseAndPrepare(query, clientState, isInternal, true);
+    }
+
+    public static Prepared parseAndPrepare(String query, ClientState clientState, boolean isInternal, boolean measure) throws RequestValidationException
     {
         CQLStatement.Raw raw = parseStatement(query);
 
@@ -441,7 +446,10 @@ public class QueryProcessor implements QueryHandler
             res = new Prepared(statement, "", fullyQualified, keyspace);
         else
             res = new Prepared(statement, query, fullyQualified, keyspace);
-        res.pstmntSize = measurePstmnt(res);
+
+        // Some prepared statements will not be cached and therefore do not require a pre-computed size.
+        if (measure)
+            res.pstmntSize = measurePstmnt(res);
 
         return res;
     }
diff --git a/src/java/org/apache/cassandra/transport/messages/BatchMessage.java b/src/java/org/apache/cassandra/transport/messages/BatchMessage.java
index 8a87efc781..d45105f109 100644
--- a/src/java/org/apache/cassandra/transport/messages/BatchMessage.java
+++ b/src/java/org/apache/cassandra/transport/messages/BatchMessage.java
@@ -188,7 +188,7 @@ public class BatchMessage extends Message.Request
                 {
                     p = QueryProcessor.parseAndPrepare((String) query,
                                                        state.getClientState().cloneWithKeyspaceIfSet(options.getKeyspace()),
-                                                       false);
+                                                       false, false);
                 }
                 else
                 {