diff --git a/src/@dseries/lag.m b/src/@dseries/lag.m
index 72197f05dc01e43575dd7e42d127ded5b110b6c6..1dff613ac0a656d50e722a30c4293227fc87a715 100644
--- a/src/@dseries/lag.m
+++ b/src/@dseries/lag.m
@@ -44,7 +44,7 @@ if nargin<2
     p = 1;
 end
 
-if p<=0
+if p<0
     error('dseries::lag: Second input argument must be strictly positive! Use lead method instead.')
 end
 
diff --git a/src/@dseries/lead.m b/src/@dseries/lead.m
index 5c5a984d10e505d301c69ff3163b0b2785cd989b..de5a79a5ce0e69cf9d6118c4abd5fb8874694e81 100644
--- a/src/@dseries/lead.m
+++ b/src/@dseries/lead.m
@@ -44,7 +44,7 @@ if nargin<2
     p = 1;
 end
 
-if p<=0
+if p<0
     error('dseries::lead: Second input argument must be strictly positive! Use lag method instead.')
 end