--- my_mongodb-3.2.0p2.ebuild	2015-12-16 18:25:45.233339542 -0500
+++ my_mongodb-3.2.0p3.ebuild	2015-12-16 19:35:21.413367214 -0500
@@ -67,8 +67,21 @@
                die "Terminating ebuild."
        fi
  
-	enewgroup mongodb
-	enewuser mongodb -1 -1 /var/lib/${PN} mongodb
+        # If the user mongodb already exists we do not neeed
+        # to add these users to the system. If the user and
+        # group do not exist, we create them.
+
+        getent group mongodb > /dev/null 2&>1
+
+        if [ "$?" -eq "1" ]; then
+       	     enewgroup mongodb
+        fi
+
+        getent passwd mongodb > /dev/null 2&>1
+
+        if [ "$?" -eq "1" ]; then
+             enewuser mongodb -1 -1 /var/lib/${PN} mongodb
+        fi
 
 	# Maintainer notes
 	#