diff --git a/stdlib/LinearAlgebra/src/bidiag.jl b/stdlib/LinearAlgebra/src/bidiag.jl
index 55d3c2d5a889a..5f9a64904bd38 100644
--- a/stdlib/LinearAlgebra/src/bidiag.jl
+++ b/stdlib/LinearAlgebra/src/bidiag.jl
@@ -184,7 +184,7 @@ end
         @inbounds A.ev[A.uplo == 'U' ? i : 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 2ff3e9b423702..37503efe42518 100644
--- a/stdlib/LinearAlgebra/test/bidiag.jl
+++ b/stdlib/LinearAlgebra/test/bidiag.jl
@@ -984,4 +984,9 @@ end
     @test Tridiagonal{Float64}(B) === Tridiagonal(evf, dvf, zf)
 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