diff --git a/src/obstransform.jl b/src/obstransform.jl
index e5c6168..4952668 100644
--- a/src/obstransform.jl
+++ b/src/obstransform.jl
@@ -159,12 +159,12 @@ end
 
 # joinumobs
 
-struct JoinedData{T,N} <: AbstractDataContainer
-    datas::NTuple{N,T}
+struct JoinedData{T<:Tuple,N} <: AbstractDataContainer
+    datas::T
     ns::NTuple{N,Int}
 end
 
-JoinedData(datas) = JoinedData(datas, numobs.(datas))
+JoinedData(datas::Tuple) = JoinedData(datas, numobs.(datas))
 
 Base.length(data::JoinedData) = sum(data.ns)
 
@@ -194,7 +194,12 @@ jdata = joinumobs(data1, data2)
 getobs(jdata, 15) == 15
 ```
 """
-joinobs(datas...) = JoinedData(datas)
+joinobs(datas...) = JoinedData(cleanjoin(datas...))
+
+cleanjoin(x::JoinedData, ys...) = (x.datas..., cleanjoin(ys...)...)
+cleanjoin(x, ys...) = (x, cleanjoin(ys...)...)
+cleanjoin() = ()
+
 
 """
     shuffleobs([rng], data)
diff --git a/test/obstransform.jl b/test/obstransform.jl
index 5b6ec7a..f94ea32 100644
--- a/test/obstransform.jl
+++ b/test/obstransform.jl
@@ -94,6 +94,27 @@ end
     @test data[5:6] == [5, 6]
     data = joinobs(ones(2, 3), zeros(2, 3))
     @test data[3:4] == [[1.0, 1.0], [0.0, 0.0]]
+
+    @testset "joins of joins" begin
+        data1, data2 = 1:10, 11:20
+        data12 = joinobs(data1, data2)
+        data3 = 21:30
+        data123 = joinobs(data12, data3)
+        @test getobs(data123, 15) == 15
+        @test getobs(data123, 25) == 25
+        @test length(data123) == 30
+        @test data123.datas[1] == data1
+        @test data123.datas[2] == data2
+        @test data123.datas[3] == data3
+    end
+
+    @testset "join different types" begin
+        data1 = 1:5
+        data2 = ones(2, 3)
+        data12 = joinobs(data1, data2)
+        @test data12[3] == 3
+        @test data12[6] == [1.0, 1.0]
+    end
 end
 
 @testset "shuffleobs" begin