diff --git a/core/src/main/java/org/apache/oozie/action/hadoop/MapReduceActionExecutor.java b/core/src/main/java/org/apache/oozie/action/hadoop/MapReduceActionExecutor.java
index b8d3b09633..6381f9c5b9 100644
--- a/core/src/main/java/org/apache/oozie/action/hadoop/MapReduceActionExecutor.java
+++ b/core/src/main/java/org/apache/oozie/action/hadoop/MapReduceActionExecutor.java
@@ -474,6 +474,13 @@ protected String findYarnApplicationId(final Context context, final WorkflowActi
         }
     }
 
+    @Override
+    protected void addActionSpecificEnvVars(Map<String, String> env) {
+        // need to specify HADOOP_MAPRED_HOME for hadoop3, otherwise mapreduce jars won't be included
+        // in the launcher's CLASSPATH.
+        env.put("HADOOP_MAPRED_HOME", "${HADOOP_HOME}");
+    }
+
     /**
      * Finds a Hadoop job ID based on {@code action-data.seq} file stored on HDFS by {@link MapReduceMain}.
      */