diff --git a/rowers/interactiveplots.py b/rowers/interactiveplots.py
index d1e64a9b..5474686c 100644
--- a/rowers/interactiveplots.py
+++ b/rowers/interactiveplots.py
@@ -619,7 +619,7 @@ def interactive_otwcpchart(powerdf,promember=0):
     # there is no Paul's law for OTW
 
     # Fit the data to thee parameter CP model
-    fitfunc = lambda pars,x: pars[0]/(1+(x/pars[2])) + pars[1]/(1+(x/pars[3]))
+    fitfunc = lambda pars,x: pars[0]/(1+(x/pars[2])) + pars[1]/(1+(x/abs(pars[3])))
     errfunc = lambda pars,x,y: fitfunc(pars,x)-y
     
     p0 = [500,350,10,8000]
@@ -636,6 +636,7 @@ def interactive_otwcpchart(powerdf,promember=0):
 	p1 = [p0[0]/factor,p0[1]/factor,p0[2],p0[3]]
 
 
+    p1 = [abs(p) for p in p1]
     fitt = pd.Series(10**(4*np.arange(100)/100.))
 
     fitpower = fitfunc(p1,fitt)