diff --git a/src/iterators/bfs.jl b/src/iterators/bfs.jl
index 8947615a2..2aa86e34b 100644
--- a/src/iterators/bfs.jl
+++ b/src/iterators/bfs.jl
@@ -32,8 +32,8 @@ julia> for node in BFSIterator(g,[1,3])
 2
 ```
 """
-struct BFSIterator{S} <: VertexIterator
-    graph::AbstractGraph
+struct BFSIterator{S, T<:AbstractGraph{S}} <: VertexIterator
+    graph::T
     source::S
 end