diff --git a/src/measures/utils.jl b/src/measures/utils.jl
index a9c3a53c..b5ff5799 100644
--- a/src/measures/utils.jl
+++ b/src/measures/utils.jl
@@ -62,7 +62,7 @@ process_idxs(solution; idxs)
 Check and sanitize the species indices or names provided (`idxs`). Used in
 [`extract_last_timesteps`](@ref) and [`living_species`](@ref).
 """
-function process_idxs(solution; idxs)
+function process_idxs(solution; idxs = nothing)
     sp = get_parameters(solution).network.species
 
     if isnothing(idxs)