diff --git a/src/mapreduce.jl b/src/mapreduce.jl
index 3d657d7..51c6607 100644
--- a/src/mapreduce.jl
+++ b/src/mapreduce.jl
@@ -209,22 +209,24 @@ function _mapreduce_block!(
         T = eltype(arrays[1])
         spacing = isbitstype(T) ? max(1, div(64, sizeof(T))) : 1 # to avoid false sharing
         threadedout = similar(arrays[1], spacing * get_num_threads())
-        a = arrays[1][ParentIndex(1)]
+        iout = ParentIndex(offsets[1] + 1)
+        a = arrays[1][iout]
         if initop !== nothing
             a = initop(a)
         end
         _init_reduction!(threadedout, f, op, a)
 
         newarrays = (threadedout, Base.tail(arrays)...)
+        newoffsets = (offset(threadedout), Base.tail(offsets)...)
         _mapreduce_threaded!(
-            f, op, nothing, dims, blocks, strides, offsets, costs,
+            f, op, nothing, dims, blocks, strides, newoffsets, costs,
             newarrays, get_num_threads(), spacing, 1
         )
 
         for i in 1:get_num_threads()
             a = op(a, threadedout[(i - 1) * spacing + 1])
         end
-        arrays[1][ParentIndex(1)] = a
+        arrays[1][iout] = a
     else
         costs = costs .* .!(iszero.(strides[1]))
         # make cost of dimensions with zero stride in output array (reduction dimensions),
diff --git a/test/othertests.jl b/test/othertests.jl
index 11dc94c..44eaee9 100644
--- a/test/othertests.jl
+++ b/test/othertests.jl
@@ -161,6 +161,24 @@ end
 
         R3 = rand(T, (5, 5, 5))
         @test prod(exp, StridedView(R3)) ≈ exp(sum(StridedView(R3)))
+
+        # Large enough to exercise threaded reduction, with offsets in both views.
+        n = 2 * Strided.MINTHREADLENGTH
+        input = sview(StridedView(fill(T(2), n + 20)), 11:(n + 10))
+        for initop in (nothing, zero, x -> 3x)
+            storage = StridedView(fill(T(99), 12))
+            output = sview(storage, 5:5)
+            fill!(output, T(7))
+            if initop === nothing
+                Base.mapreducedim!(identity, +, output, input)
+            else
+                Strided._mapreducedim!(identity, +, initop, (n,), (output, input))
+            end
+            initial = initop === nothing ? T(7) : initop(T(7))
+            expected = fill(T(99), 12)
+            expected[5] = initial + T(2) * n
+            @test Array(storage) == expected
+        end
     end
 end