diff --git a/src/interval.jl b/src/interval.jl
index 023e2da..1299b09 100644
--- a/src/interval.jl
+++ b/src/interval.jl
@@ -27,14 +27,7 @@ mathematical notation, the constructed range is `(left, right)`.
 const OpenInterval{T} = Interval{:open,:open,T}
 
 Interval{L,R,T}(i::AbstractInterval) where {L,R,T} = Interval{L,R,T}(endpoints(i)...)
-function Interval{L,R}(left, right) where {L,R}
-    # TODO: Replace the retrun value with `Interval{L,R}(promote(left,right)...)`. (#93)
-    T = promote_type(typeof(left), typeof(right))
-    if !isconcretetype(T)
-        Base.depwarn("`Promotion to a concrete type failed and will error in the next release; consider constructing this interval as `Interval{L,R,$(typejoin(typeof(left),typeof(right)))}(left, right)`.", :Interval)
-    end
-    Interval{L,R,T}(left,right)
-end
+Interval{L,R}(left, right) where {L,R} = Interval{L,R}(promote(left,right)...)
 Interval{L,R}(left::T, right::T) where {L,R,T} = Interval{L,R,T}(left, right)
 Interval(left, right) = ClosedInterval(left, right)
 
diff --git a/test/runtests.jl b/test/runtests.jl
index 1f59a37..4bb8567 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -4,6 +4,7 @@ using Dates
 using Statistics
 import Statistics: mean
 using Random
+using Unitful
 
 import IntervalSets: Domain, endpoints, closedendpoints, TypedEndpointsInterval
 
@@ -22,14 +23,16 @@ closedendpoints(I::MyUnitInterval) = (I.isleftclosed,I.isrightclosed)
 struct IncompleteInterval <: AbstractInterval{Int} end
 
 @testset "IntervalSets" begin
-    @test isempty(detect_ambiguities(IntervalSets, Base, Core))
+    @test isempty(detect_ambiguities(IntervalSets))
 
     @test ordered(2, 1) == (1, 2)
     @test ordered(1, 2) == (1, 2)
     @test ordered(Float16(1), 2) == (1, 2)
 
     @testset "Basic Closed Sets" begin
-        @test_throws ArgumentError :a .. "b"
+        @test_throws ErrorException :a .. "b"
+        @test_throws ErrorException 1 .. missing
+        @test_throws ErrorException 1u"m" .. 2u"s"
         I = 0..3
         @test I === ClosedInterval(0,3) === ClosedInterval{Int}(0,3) ===
                  Interval(0,3)
@@ -139,6 +142,13 @@ struct IncompleteInterval <: AbstractInterval{Int} end
         @test_throws MethodError duration(1.2..2.4)
     end
 
+    @testset "Unitful interval" begin
+        @test 1.5u"m" in 1u"m" .. 2u"m"
+        @test 1500u"μm" in 1u"mm" .. 1u"m"
+        @test !(500u"μm" in 1u"mm" .. 1u"m")
+        @test 1u"m" .. 2u"m" == 1000u"mm" .. 2000u"mm"
+    end
+
     @testset "Day interval" begin
         A = Date(1990, 1, 1); B = Date(1990, 3, 1)
         @test width(ClosedInterval(A, B)) == Dates.Day(59)
@@ -640,12 +650,6 @@ struct IncompleteInterval <: AbstractInterval{Int} end
         @test I ∩ (0.0..0.5) === 0.0..0.5
     end
 
-    @testset "Missing endpoints" begin
-        # TODO: Remove this testset in the next breaking release (#94)
-        @test ismissing(2 in 1..missing)
-        @test_broken ismissing(2 in missing..1)  # would be fixed by julialang#31171
-    end
-
     @testset "in" begin
         @test in(0.1, 0.0..1.0) == true
         @test in(0.0, 0.0..1.0) == true