diff --git a/src/axis.jl b/src/axis.jl
index 29ea4222..3e7e27cc 100644
--- a/src/axis.jl
+++ b/src/axis.jl
@@ -140,8 +140,11 @@ const NotShapedOrPartitionedAxis = Union{Axis{IdxMap}, FlatAxis, NullAxis} where
 
 Base.merge(axs::Axis...) = Axis(merge(indexmap.(axs)...))
 
+# TODO: broken for FlatAxis
 Base.firstindex(ax::AbstractAxis) = first(viewindex(first(indexmap(ax))))
 Base.lastindex(ax::AbstractAxis) = last(viewindex(last(indexmap(ax))))
+Base.length(ax::AbstractAxis) = lastindex(ax) - firstindex(ax) + 1
+Base.length(ax::NullorFlatAxis) = error("NullorFlatAxis has no length")
 
 Base.keys(ax::AbstractAxis) = keys(indexmap(ax))
 
diff --git a/src/componentarray.jl b/src/componentarray.jl
index ea09fa84..955ed230 100644
--- a/src/componentarray.jl
+++ b/src/componentarray.jl
@@ -235,6 +235,19 @@ last_index(x) = last(x)
 last_index(x::ViewAxis) = last_index(viewindex(x))
 last_index(x::AbstractAxis) = last_index(last(indexmap(x)))
 
+# length information is in Axis, use it to make SVector creation type stable
+@inline _hasNullOrFlatAxis(ca) = any(map(ax -> ax isa NullorFlatAxis, getaxes(ca)))
+function Base.length(ca::ComponentArray) 
+    # vca2 = vcat(ca2', ca2') #has not length - is it a valid ComponentVector
+    # or rather a Vector<ComponentVector>
+    _hasNullOrFlatAxis(ca) && return(length(getdata(ca)))
+    prod(length.(getaxes(ca)))
+end
+function Base.size(ca::ComponentArray) 
+    _hasNullOrFlatAxis(ca) && return(size(getdata(ca)))
+    map(length, getaxes(ca))
+end
+
 # Reduce singleton dimensions
 remove_nulls() = ()
 remove_nulls(x1, args...) = (x1, remove_nulls(args...)...)
diff --git a/test/runtests.jl b/test/runtests.jl
index a863af41..7b27cec5 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -598,6 +598,14 @@ end
     @test convert(Cholesky{Float32,Matrix{Float32}}, chol).factors isa Matrix{Float32}
 end
 
+@testset "length typestable" begin
+    # function boundary, so that cv is type-inferred
+    test_create_svector = (cv) -> SVector{length(cv)}(cv)
+    @inferred test_create_svector(ComponentVector(a=1:3));
+    test_create_smatrix = (cmat) -> SMatrix{size(cmat)...}(cmat)
+    @test (@inferred test_create_smatrix(cmat)) isa SMatrix
+end;
+
 @testset "Autodiff" begin
     include("autodiff_tests.jl")
 end
\ No newline at end of file