diff --git a/src/component_functions.jl b/src/component_functions.jl
index 38ba8a68..06751882 100644
--- a/src/component_functions.jl
+++ b/src/component_functions.jl
@@ -964,7 +964,7 @@ function _fill_defaults(T, @nospecialize(kwargs))
     #### External Inputs
     ####
     if haskey(dict, :extin)
-        @assert dict[:extin] isa Vector{<:SymbolicIndex}
+        @assert dict[:extin] isa Union{Nothing, Vector{<:SymbolicIndex}}
     else
         dict[:extin] = nothing
     end
diff --git a/src/external_inputs.jl b/src/external_inputs.jl
index 4f65ced8..c4afda48 100644
--- a/src/external_inputs.jl
+++ b/src/external_inputs.jl
@@ -13,11 +13,13 @@ function ExtMap(im::IndexManager)
     isempty(map) && error("There are no external inputs.")
 
     for (vi, vm) in pairs(im.vertexm)
+        has_external_input(vm) || continue
         for (i, si) in pairs(vm.extin)
             map[im.v_ext[vi][i]] = _symidx_to_extidx(im, si)
         end
     end
     for (ei, em) in pairs(im.edgem)
+        has_external_input(em) || continue
         for (i, si) in pairs(em.extin)
             map[im.e_ext[ei][i]] = _symidx_to_extidx(im, si)
         end
diff --git a/src/symbolicindexing.jl b/src/symbolicindexing.jl
index 8adb8d30..f5b46bcd 100644
--- a/src/symbolicindexing.jl
+++ b/src/symbolicindexing.jl
@@ -514,7 +514,7 @@ function _get_observed_f(nw::Network, cf::EdgeModel, eidx)
     @closure (u, outbuf, aggbuf, extbuf, p, t) -> begin
         ins = (view(outbuf, esrcr), view(outbuf, edstr))
         if has_external_input(cf)
-            (ins..., view(aggbuf, aggr), view(extbuf, extr))
+            (ins..., view(extbuf, extr))
         end
         cf.obsf(ret, view(u, ur), ins..., view(p, pr), t)
         ret