diff --git a/src/io.jl b/src/io.jl
index f2a777a..96d3754 100644
--- a/src/io.jl
+++ b/src/io.jl
@@ -13,15 +13,8 @@ function par2ystr(par::AbstractParametersVector, txt::Vector{String}; show_info:
     end
 end
 
-function equals_with_missing(a, b)
-    if ismissing(a) && ismissing(b)
-        return true
-    elseif ismissing(a) || ismissing(b)
-        return false
-    else
-        return a == b
-    end
-end
+# isequal treats missing==missing and NaN==NaN as true, unlike ==
+equals_with_missing(a, b) = isequal(a, b)
 
 function YAML._print(io::IO, value::Missing, level::Int=0, ignore_level::Bool=false)
     return println(io, "~")
diff --git a/src/utils.jl b/src/utils.jl
index 0c4f548..1da60a0 100644
--- a/src/utils.jl
+++ b/src/utils.jl
@@ -41,7 +41,7 @@ function Base.diff(p1::AbstractParametersVector, p2::AbstractParametersVector)
     end
     for key in commonkeys
         v1 = p1[key]
-        v2 = p1[key]
+        v2 = p2[key]
         if typeof(v1) !== typeof(v2)
             error("$key is of different type")
         elseif typeof(v1) <: AbstractParameters