diff --git a/misc/memory_stats.rb b/misc/memory_stats.rb
index <HASH>..<HASH> 100755
--- a/misc/memory_stats.rb
+++ b/misc/memory_stats.rb
@@ -30,12 +30,25 @@ class MemoryStats
 	end
 	
 	def start
+		some_private_dirty_rss_cannot_be_determined = false
 		processes = list_processes(:exe => PlatformInfo::HTTPD)
+		some_private_dirty_rss_cannot_be_determined = processes.any? do |p|
+			p.private_dirty_rss.nil?
+		end
 		print_process_list_stats(processes)
 		
 		puts
 		processes = list_processes(:match => /^(Passenger|Rails) /)
+		some_private_dirty_rss_cannot_be_determined ||= processes.any? do |p|
+			p.private_dirty_rss.nil?
+		end
 		print_process_list_stats(processes)
+
+		if ::Process.uid != 0 && some_private_dirty_rss_cannot_be_determined
+			puts
+			puts "*** WARNING: Please run this tool as root, otherwise it " <<
+				"can't determine the private dirty RSS of processes."
+		end
 	end
 	
 	# Returns a list of Process objects that match the given search criteria.
Memory statistics tool: warn if it's not running as root.