diff --git a/src/equations.jl b/src/equations.jl
index 9739f51de..62c5934e2 100644
--- a/src/equations.jl
+++ b/src/equations.jl
@@ -33,7 +33,7 @@ end
 ###
 _nameof(s) = nameof(s)
 _nameof(s::Union{Int, Symbol}) = s
-abstract type StateMachineOperator end
+abstract type StateMachineOperator <: Real end
 hide_lhs(_::StateMachineOperator) = true
 struct InitialState <: StateMachineOperator
     s