diff --git a/stdlib/SparseArrays/src/linalg.jl b/stdlib/SparseArrays/src/linalg.jl
index 6e9a751dd4306..ad8ffb2b14f63 100644
--- a/stdlib/SparseArrays/src/linalg.jl
+++ b/stdlib/SparseArrays/src/linalg.jl
@@ -968,7 +968,7 @@ function copyinds!(C::SparseMatrixCSC, A::SparseMatrixCSC)
 end
 
 # multiply by diagonal matrix as vector
-function mul!(C::SparseMatrixCSC, A::SparseMatrixCSC, D::Diagonal{<:Vector})
+function mul!(C::SparseMatrixCSC, A::SparseMatrixCSC, D::Diagonal{T, <:Vector}) where T
     m, n = size(A)
     b    = D.diag
     (n==length(b) && size(A)==size(C)) || throw(DimensionMismatch())
@@ -982,7 +982,7 @@ function mul!(C::SparseMatrixCSC, A::SparseMatrixCSC, D::Diagonal{<:Vector})
     C
 end
 
-function mul!(C::SparseMatrixCSC, D::Diagonal{<:Vector}, A::SparseMatrixCSC)
+function mul!(C::SparseMatrixCSC, D::Diagonal{T, <:Vector}, A::SparseMatrixCSC) where T
     m, n = size(A)
     b    = D.diag
     (m==length(b) && size(A)==size(C)) || throw(DimensionMismatch())
diff --git a/stdlib/SparseArrays/test/sparse.jl b/stdlib/SparseArrays/test/sparse.jl
index 0c17946d7a5d8..416cbffac27cf 100644
--- a/stdlib/SparseArrays/test/sparse.jl
+++ b/stdlib/SparseArrays/test/sparse.jl
@@ -8,6 +8,7 @@ using LinearAlgebra
 using Base.Printf: @printf
 using Random
 using Test: guardseed
+using InteractiveUtils: @which
 
 @testset "issparse" begin
     @test issparse(sparse(fill(1,5,5)))
@@ -2295,4 +2296,15 @@ end
     @test typeof(a) === typeof(na)
 end
 
+#PR #29045
+@testset "Issue #28934" begin
+    A = sprand(5,5,0.5)
+    D = Diagonal(rand(5))
+    C = copy(A)
+    m1 = @which mul!(C,A,D)
+    m2 = @which mul!(C,D,A)
+    @test m1.module == SparseArrays
+    @test m2.module == SparseArrays
+end
+
 end # module