diff --git a/src/@dseries/isnan.m b/src/@dseries/isnan.m
index b6fd5ada59f9a0154e30c7c0aaaf58fbde8533aa..a05b016d715ba5c11175804dd4aca8a45981de55 100644
--- a/src/@dseries/isnan.m
+++ b/src/@dseries/isnan.m
@@ -1,7 +1,7 @@
 function b = isnan(o) % --*-- Unitary tests --*--
 
 % Returns an array of logicals (true/false). Element (t,i) is true iff the i-th variable at
-% period number t is not a NaN.
+% period number t is a NaN.
 %
 % INPUTS
 % - o [dseries]    with N variables and T periods.