diff --git a/watpy/wave/wave.py b/watpy/wave/wave.py
index 86714e68a6951302357d288c1e8c2745447adc81..b1eb5a73a3c3b8a23a3af94e4c521eb6479ad00d 100644
--- a/watpy/wave/wave.py
+++ b/watpy/wave/wave.py
@@ -437,11 +437,11 @@ class wave(object):
         M        = self.prop["mass"]
         R        = self.prop['detector.radius']
         headstr = write_headstr(R,M)
+        key = write_key(self.prop['lmode'], self.prop['mmode'], R)
         if var == 'Psi4':
             headstr += "u/M:0 RePsi4/M:1 ImPsi4/M:2 Momega:3 A/M:4 phi:5 t:6"
             data = np.c_[self.time_ret()/M, self.p4.real*R/M, self.p4.imag*R/M, M*self.phase_diff1(var),
                      self.amplitude(var)*R/M, self.phase(var), self.time]
-            key = write_key(self.prop['lmode'], self.prop['mmode'], R)
             #fname = 'Rpsi4_l%d_m%d_r%05d.txt' % (self.prop['lmode'], self.prop['mmode'], R)
             fname = 'Rpsi4_'+key+'.txt'
         elif var == 'h':