diff --git a/src/@dseries/lag_.m b/src/@dseries/lag_.m
index e78b658d06df9cab13b6046c8e992a405278a4ad..9c2487c50056e0c91d449e6d9bbe8f6c5f9ac245 100644
--- a/src/@dseries/lag_.m
+++ b/src/@dseries/lag_.m
@@ -46,8 +46,8 @@ if nargin<2
 end
 
 % Check second input argument
-if p<=0
-    error('dseries:WrongInputArguments','Second input argument must be strictly positive! Use lead method instead.')
+if p<0
+    error('dseries:WrongInputArguments','Second input argument must be non negative! Use lead method instead.')
 end
 
 if ~isint(p)
diff --git a/src/@dseries/lead_.m b/src/@dseries/lead_.m
index 2576a30df4039106e732c633bd1d2fb93cf42753..1a098bf049013f91f4e026d2c3e16d6ed4eda9d4 100644
--- a/src/@dseries/lead_.m
+++ b/src/@dseries/lead_.m
@@ -46,8 +46,8 @@ if nargin<2
 end
 
 % Check second input argument
-if p<=0
-    error('dseries:WrongInputArguments','Second input argument must be strictly positive! Use lag method instead.')
+if p<0
+    error('dseries:WrongInputArguments','Second input argument must be non negative! Use lag method instead.')
 end
 
 if ~isint(p)