diff --git a/src/chains.jl b/src/chains.jl
index c5966c51..6138bbbc 100644
--- a/src/chains.jl
+++ b/src/chains.jl
@@ -54,18 +54,20 @@ end
 function Chains(
         val::AbstractArray{A,3},
         parameter_names::Vector{String} = map(i->"Param$i", 1:size(val, 2)),
-        name_map = copy(DEFAULT_MAP);
+        name_map_original = copy(DEFAULT_MAP);
         start::Int=1,
         thin::Int=1,
         evidence = missing,
         info::NamedTuple=NamedTuple(),
         sorted::Bool=true) where {A<:Union{Real, Union{Missing, Real}}}
-
     # If we received an array of pairs, convert it to a dictionary.
-    if typeof(name_map) <: Array
-        name_map = Dict(name_map)
-    elseif typeof(name_map) <: NamedTuple
-        name_map = _namedtuple2dict(name_map)
+    name_map = if typeof(name_map_original) <: Dict
+        # Copying can avoid state mutation.
+        deepcopy(name_map_original)
+    elseif typeof(name_map_original) <: Array
+        Dict(deepcopy(name_map_original))
+    elseif typeof(name_map_original) <: NamedTuple
+        _namedtuple2dict(name_map_original)
     end
 
     # Make sure that we have a :parameters index.
diff --git a/src/summarize.jl b/src/summarize.jl
index d043dcb5..2d87a140 100644
--- a/src/summarize.jl
+++ b/src/summarize.jl
@@ -47,7 +47,7 @@ function Base.show(io::IO, c::ChainDataFrame)
 end
 
 Base.getindex(c::ChainDataFrame, args...) = getindex(c.df, args...)
-Base.getindex(c::ChainDataFrame, s::Union{Symbol, Vector{Symbol}}) = c.df[s]
+Base.getindex(c::ChainDataFrame, s::Union{Symbol, Vector{Symbol}}) = c.df[:, s]
 Base.isequal(cs1::Vector{ChainDataFrame}, cs2::Vector{ChainDataFrame}) = isequal.(cs1, cs2)
 Base.isequal(c1::ChainDataFrame, c2::ChainDataFrame) = isequal(c1, c2)
 
@@ -75,13 +75,13 @@ end
 function Base.getindex(c::ChainDataFrame,
         s1::Vector{Symbol},
         s2::Union{Symbol, Vector{Symbol}})
-    return c.df[map(x -> x in s1, c.df.parameters), s2]
+    return c.df[map(x -> x in s1, c.df[:, :parameters]), s2]
 end
 
 function Base.getindex(c::ChainDataFrame,
         s1::Symbol,
         s2::Union{Symbol, Vector{Symbol}})
-    return c.df[c.df.parameters .== s1, s2]
+    return c.df[c.df[:, :parameters] .== s1, s2]
 end