diff --git a/src/sizes.jl b/src/sizes.jl
index 1c76881..bb3d44f 100644
--- a/src/sizes.jl
+++ b/src/sizes.jl
@@ -46,7 +46,12 @@ function _getscalar(x, sizes::Sizes, k::Int)
 end
 
 function _setscalar!(x, value, sizes::Sizes, k::Int)
-    return x[sizes.storage_offset[k]+1] = value
+    # Use a 1-element view + broadcast so this works on GPU storage as well as
+    # `Vector{Float64}`. Direct `x[idx] = value` is a scalar setindex which
+    # GPUArrays disallows by default.
+    pos = _scalar_pos(sizes, k)
+    view(x, reshape(pos:pos, ())) .= value
+    return value
 end
 
 """