diff --git a/hadoop-common-project/hadoop-common/CHANGES.txt b/hadoop-common-project/hadoop-common/CHANGES.txt
index f3a02377d9..1a8c41d099 100644
--- a/hadoop-common-project/hadoop-common/CHANGES.txt
+++ b/hadoop-common-project/hadoop-common/CHANGES.txt
@@ -138,6 +138,9 @@ Trunk (Unreleased)
     HADOOP-11025. hadoop-daemons.sh should just call hdfs directly (Masatake
     Iwasaki via aw)
 
+    HADOOP-11150. hadoop command should show the reason on failure by 
+    invalid COMMAND or CLASSNAME (Masatake Iwasaki via aw)
+
   BUG FIXES
 
     HADOOP-9451. Fault single-layer config if node group topology is enabled.
diff --git a/hadoop-common-project/hadoop-common/src/main/bin/hadoop-functions.sh b/hadoop-common-project/hadoop-common/src/main/bin/hadoop-functions.sh
index 4f75a7ccf5..b5d4b1c12b 100644
--- a/hadoop-common-project/hadoop-common/src/main/bin/hadoop-functions.sh
+++ b/hadoop-common-project/hadoop-common/src/main/bin/hadoop-functions.sh
@@ -286,6 +286,9 @@ function hadoop_validate_classname
   shift 1
 
   if [[ ! ${class} =~ \. ]]; then
+    # assuming the arg is typo of command if it does not conatain ".".
+    # class belonging to no package is not allowed as a result.
+    hadoop_error "ERROR: ${class} is not COMMAND nor fully qualified CLASSNAME."
     return 1
   fi
   return 0