diff --git a/stdlib/LinearAlgebra/src/bidiag.jl b/stdlib/LinearAlgebra/src/bidiag.jl
index a5f0af4720cf5..e6753a49d8b31 100644
--- a/stdlib/LinearAlgebra/src/bidiag.jl
+++ b/stdlib/LinearAlgebra/src/bidiag.jl
@@ -166,7 +166,7 @@ end
         @inbounds A.ev[j] = x
     elseif !iszero(x)
         throw(ArgumentError(LazyString(lazy"cannot set entry ($i, $j) off the ",
-            istriu(A) ? "upper" : "lower", " bidiagonal band to a nonzero value ", x)))
+            A.uplo == 'U' ? "upper" : "lower", " bidiagonal band to a nonzero value ", x)))
     end
     return x
 end
diff --git a/stdlib/LinearAlgebra/test/bidiag.jl b/stdlib/LinearAlgebra/test/bidiag.jl
index d13009780b975..48b498374b364 100644
--- a/stdlib/LinearAlgebra/test/bidiag.jl
+++ b/stdlib/LinearAlgebra/test/bidiag.jl
@@ -822,4 +822,9 @@ end
     @test all(iszero, diag(B, 1))
 end
 
+@testset "off-band indexing error" begin
+    B = Bidiagonal(Vector{BigInt}(undef, 4), Vector{BigInt}(undef,3), :L)
+    @test_throws "cannot set entry" B[1,2] = 4
+end
+
 end # module TestBidiagonal