diff --git a/src/stats/histograms.jl b/src/stats/histograms.jl
index 334c2a0e..26ed751a 100644
--- a/src/stats/histograms.jl
+++ b/src/stats/histograms.jl
@@ -327,10 +327,10 @@ Ref: [http://www.jmlr.org/papers/volume11/ben-haim10a/ben-haim10a.pdf](http://ww
     using Plots
     plot(o)
 """
-struct KHist{T} <: HistogramStat{Number}
+struct KHist{T, E<:Extrema{T}} <: HistogramStat{Number}
     bins::Vector{KHistBin{T}}
     b::Int
-    ex::Extrema{T}
+    ex::E
 end
 KHist(b::Int, T::Type = Float64) = KHist(KHistBin{T}[], b, Extrema(T))
 
diff --git a/src/stats/stats.jl b/src/stats/stats.jl
index 24a11015..3eb00f88 100644
--- a/src/stats/stats.jl
+++ b/src/stats/stats.jl
@@ -361,12 +361,13 @@ Maximum and minimum.
     maximum(o)
     minimum(o)
 """
-mutable struct Extrema{T} <: OnlineStat{Number}
+mutable struct Extrema{T,S} <: OnlineStat{S}
     min::T
     max::T
     n::Int
 end
-Extrema(T::Type{<:Number} = Float64) = Extrema{T}(typemax.(T), typemin.(T), 0)
+Extrema(T::Type{<:Number} = Float64) = Extrema{T,Number}(typemax.(T), typemin.(T), 0)
+Extrema(T::Type) = Extrema{T,T}(typemax.(T), typemin.(T), 0)
 Extrema(initmin::T, initmax::T) where {T} = Extrema{T}(initmin, initmax, 0)
 function _fit!(o::Extrema, y)
     o.min = min(o.min, y)
diff --git a/test/runtests.jl b/test/runtests.jl
index 939df830..8492219e 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -112,6 +112,10 @@ end
     @test value(fit!(Extrema(Int), z)) == extrema(z)
 
     @test ==(mergevals(Extrema(), y, y2)...)
+
+    o = fit!(Extrema(Date), Date(2010):Day(1):Date(2011))
+    @test minimum(o) == Date(2010)
+    @test maximum(o) == Date(2011)
 end
 #-----------------------------------------------------------------------# Fit[Dist]
 @testset "Fit[Dist]" begin