diff --git a/src/FillArrays.jl b/src/FillArrays.jl
index 7ca7b78e..1a8cd734 100644
--- a/src/FillArrays.jl
+++ b/src/FillArrays.jl
@@ -578,7 +578,6 @@ cumsum(x::AbstractZerosVector{Bool}) = x
 cumsum(x::AbstractOnesVector{II}) where II<:Integer = convert(AbstractVector{II}, oneto(length(x)))
 cumsum(x::AbstractOnesVector{Bool}) = oneto(length(x))
 
-
 #########
 # Diff
 #########
diff --git a/src/fillalgebra.jl b/src/fillalgebra.jl
index 99fda41c..06436d74 100644
--- a/src/fillalgebra.jl
+++ b/src/fillalgebra.jl
@@ -5,7 +5,6 @@ vec(a::AbstractFill) = fillsimilar(a, length(a))
 ## Transpose/Adjoint
 # cannot do this for vectors since that would destroy scalar dot product
 
-
 transpose(a::Union{AbstractOnesMatrix, AbstractZerosMatrix}) = fillsimilar(a, reverse(axes(a)))
 adjoint(a::Union{AbstractOnesMatrix, AbstractZerosMatrix}) = fillsimilar(a, reverse(axes(a)))
 transpose(a::FillMatrix{T}) where T = Fill{T}(transpose(a.value), reverse(a.axes))
@@ -30,6 +29,9 @@ end
 reverse(A::AbstractFill; dims=:) = A
 
 ## Algebraic identities
+@inline checkdimensionmismatch(a::AbstractVecOrMat, b::AbstractVecOrMat) = axes(a, 2) ≠ axes(b, 1) && throw(DimensionMismatch("A has axes $(axes(a)) but B has axes $(axes(b))"))
+@inline productaxes(a::AbstractVecOrMat, b::AbstractVector) = (axes(a, 1),)
+@inline productaxes(a::AbstractVecOrMat, b::AbstractMatrix) = (axes(a, 1), axes(b, 2))
 
 # Default outputs, can overload to customize
 mult_fill(a, b, val, ax) = Fill(val, ax)