diff --git a/src/mcs/defmcs.jl b/src/mcs/defmcs.jl
index 3e1313bac..200793b25 100644
--- a/src/mcs/defmcs.jl
+++ b/src/mcs/defmcs.jl
@@ -165,7 +165,7 @@ macro defsim(expr)
         # TBD: need to generalize this to support other methods
         return :(Simulation{$simdatatype}(
                     [$(_rvs...)],
-                    [$(_transforms...)],  
+                    TransformSpec[$(_transforms...)],  
                     Tuple{Symbol, Symbol}[$(_saves...)],
                     $data))
     end
diff --git a/src/mcs/mcs_types.jl b/src/mcs/mcs_types.jl
index 906536970..b83c0938f 100644
--- a/src/mcs/mcs_types.jl
+++ b/src/mcs/mcs_types.jl
@@ -161,6 +161,15 @@ mutable struct Simulation{T}
     end
 end
 
+"""
+    Simulation{T}() where T <: AbstractSimulationData
+
+Allow creation of an "empty" Simulation instance.
+"""
+function Simulation{T}() where T <: AbstractSimulationData
+    Simulation{T}([], TransformSpec[], Tuple{Symbol, Symbol}[], T())
+end
+
 """
     set_payload!(sim::Simulation, payload)