Index: trunk/FACT++/src/ratecontrol.cc
===================================================================
--- trunk/FACT++/src/ratecontrol.cc	(revision 17166)
+++ trunk/FACT++/src/ratecontrol.cc	(revision 17167)
@@ -482,5 +482,6 @@
         avg /= fCurrentsMed.size();
         rms /= fCurrentsMed.size();
-        rms = sqrt(rms-avg*avg);
+        rms -= avg*avg;
+        rms = rms<0 ? 0 : sqrt(rms);
 
         double avg_dev = 0;