diff --git a/src/mapsignal.jl b/src/mapsignal.jl
index ca04a5c..32330aa 100644
--- a/src/mapsignal.jl
+++ b/src/mapsignal.jl
@@ -37,8 +37,6 @@ SignalTrait(x::Type{<:MapSignal{<:Any,<:Any,<:Any,T,Fs,L}}) where {Fs,T,L} =
 nchannels(x::MapSignal) = length(x.val)
 framerate(x::MapSignal) = x.framerate
 
-isnumbers(::Tuple{<:Number}) = true
-isnumbers(xs) = false
 function duration(x::MapSignal)
     durs = duration.(x.padded_signals)
     Ns = nframes_helper.(x.padded_signals)
@@ -146,14 +144,13 @@ function OperateOn(fn,xs...;
         bychannel)
 end
 
-maxlen(x::Extended,y::Number) = max(x.len,y)
-maxlen(x::Extended,y::Extended) = max(x.len,y.len)
-maxlen(x::Extended,y::Infinite) = x.len
-maxlen(x::NumberExtended,y) = y
-maxlen(x::NumberExtended,y::Extended) = y.len
-maxlen(x,y) = max(x,y)
-maxlen(x,y::Extended) = max(x,y.len)
-maxlen(x,y::NumberExtended) = x
+tolen(x::Extended) = x.len
+tolen(x::Number) = x
+tolen(x::NumberExtended) = 0
+tolen(x::InfiniteLength) = inflen
+tolen(x::Missing) = missing
+maxlen(x,y) = max(tolen(x),tolen(y))
+maxlen(x::NumberExtended,y::NumberExtended) = x
 nframes_helper(x::MapSignal) = reduce(maxlen,nframes_helper.(x.signals))
 
 """
diff --git a/test/runtests.jl b/test/runtests.jl
index a928e39..d9a31f3 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -218,9 +218,15 @@ progress = Progress(total_test_groups,desc="Running tests...")
 
             @test Extend(x,one) |> nframes == inflen
             @test Mix(Extend(x,one),y) |> nframes == 15
+            @test Mix(y,Extend(x,one)) |> nframes == 15
             @test Mix(Pad(x,one),y) |> nframes |> isinf
             @test Mix(1,rand(10,2)) |> nframes == 10
+            @test Mix(1,Extend(rand(10,2),zero)) |> nframes == 10
+            @test Mix(rand(10,2),1) |> nframes == 10
+            @test Mix(Extend(rand(10,2),zero),1) |> nframes == 10
             @test Mix(sin,1,rand(10,2)) |> nframes |> isinf
+            @test Mix(1,sin,rand(10,2)) |> nframes |> isinf
+            @test Mix(1,rand(10,2),sin) |> nframes |> isinf
         end
     end
     next!(progress)
@@ -629,6 +635,8 @@ progress = Progress(total_test_groups,desc="Running tests...")
             "100×2 Array{Float64,2}: … (10.0 Hz) |>\n    Append(50×2 Array{Float64,2}: … (10.0 Hz))"
         @test x |> Pad(zero) |> showstring ==
             "100×2 Array{Float64,2}: … (10.0 Hz) |> Pad(zero)"
+        @test x |> Extend(zero) |> showstring ==
+            "100×2 Array{Float64,2}: … (10.0 Hz) |> Extend(zero)"
         @test x |> Filt(Lowpass,3Hz) |> showstring ==
             "100×2 Array{Float64,2}: … (10.0 Hz) |> Filt(Lowpass,3 Hz)"
         @test x |> Normpower |> showstring ==