diff --git a/src/a_star.jl b/src/a_star.jl
index 8c4cd29..7a2bf3c 100644
--- a/src/a_star.jl
+++ b/src/a_star.jl
@@ -37,7 +37,7 @@ end
                     s::Integer,                       
                     t::Integer,                       
                     distmx::AbstractMatrix{T}=LightGraphs.weights(g),
-                    heuristic::Function = n -> zero(T)) where {T, U}
+                    heuristic::Function = (u,v) -> zero(T)) where {T, U}
 
 High level function - implementation of A star search algorithm:
 (https://en.wikipedia.org/wiki/A*_search_algorithm). 
@@ -56,7 +56,7 @@ function a_star_algorithm(g::LightGraphs.AbstractGraph{U},  # the g
                           s::Integer,           # the start vertex
                           t::Integer,           # the end vertex
                           distmx::AbstractMatrix{T}=LightGraphs.weights(g),
-                          heuristic::Function = n -> zero(T)) where {T, U}
+                          heuristic::Function = (u,v) -> zero(T)) where {T, U}
     checkbounds(distmx, Base.OneTo(nv(g)), Base.OneTo(nv(g)))
     frontier = DataStructures.PriorityQueue{Tuple{T, U},T}()
     frontier[(zero(T), U(s))] = zero(T)
diff --git a/src/routing.jl b/src/routing.jl
index 3e586a5..ebbd0e2 100644
--- a/src/routing.jl
+++ b/src/routing.jl
@@ -155,7 +155,7 @@ calculate_distance(m::OpenStreetMapX.MapData, weights::SparseArrays.SparseMatrix
 
 function find_route(m::OpenStreetMapX.MapData, node0::Int, node1::Int, 
                     weights::SparseArrays.SparseMatrixCSC{Float64,Int64};
-                    routing::Symbol = :astar, heuristic::Function = n -> zero(Float64),
+                    routing::Symbol = :astar, heuristic::Function = (u,v) -> zero(Float64),
                     get_distance::Bool = false, get_time::Bool = false)
     result = Any[]
 	start_vertex = m.v[node0]
@@ -206,7 +206,7 @@ end
 
 function find_route(m::OpenStreetMapX.MapData, node0::Int, node1::Int, node2::Int, 
                     weights::SparseArrays.SparseMatrixCSC{Float64,Int64};
-                    routing::Symbol = :astar, heuristic::Function = n -> zero(Float64), 
+                    routing::Symbol = :astar, heuristic::Function = (u,v) -> zero(Float64), 
                     get_distance::Bool = false, get_time::Bool = false)
     result = Any[]
     route1 = OpenStreetMapX.find_route(m, node0, node1, weights,