diff --git a/src/core/time_arrays.jl b/src/core/time_arrays.jl
index 272b202cc..68db3657c 100644
--- a/src/core/time_arrays.jl
+++ b/src/core/time_arrays.jl
@@ -244,7 +244,7 @@ end
 
 function Base.getindex(mat::TimestepMatrix{FixedTimestep{FIRST, STEP, LAST}, T_data, 1}, ts::TimestepValue{T_time}, idx::AnyIndex) where {T_data, FIRST, STEP, LAST, T_time} 
 	t = _get_time_value_position([FIRST:STEP:LAST...], ts)
-	mat.data isa SubArray ? view_offset = mat.data.indices[1][1] + 1 : view_offset = 0
+	mat.data isa SubArray ? view_offset = mat.data.indices[1][1] - 1 : view_offset = 0
 	t = t - view_offset
 	data = mat.data[t, idx]
 	_missing_data_check(data, t)
@@ -252,7 +252,7 @@ end
 
 function Base.getindex(mat::TimestepMatrix{VariableTimestep{TIMES}, T_data, 1}, ts::TimestepValue{T_time}, idx::AnyIndex) where {T_data, TIMES, T_time}
 	t = _get_time_value_position(TIMES, ts)
-	mat.data isa SubArray ? view_offset = mat.data.indices[1][1] + 1 : view_offset = 0
+	mat.data isa SubArray ? view_offset = mat.data.indices[1][1] - 1 : view_offset = 0
 	t = t - view_offset
 	data = mat.data[t, idx]
 	_missing_data_check(data, t)
@@ -267,7 +267,7 @@ end
 
 function Base.getindex(mat::TimestepMatrix{FixedTimestep{FIRST, STEP, LAST}, T_data, 2}, idx::AnyIndex, ts::TimestepValue{T_time}) where {T_data, FIRST, STEP, LAST, T_time} 
 	t = _get_time_value_position([FIRST:STEP:LAST...], ts)
-	mat.data isa SubArray ? view_offset = mat.data.indices[2][1] + 1 : view_offset = 0
+	mat.data isa SubArray ? view_offset = mat.data.indices[2][1] - 1 : view_offset = 0
 	t = t - view_offset
 	data = mat.data[idx, t]
 	_missing_data_check(data, t)
@@ -275,7 +275,7 @@ end
 
 function Base.getindex(mat::TimestepMatrix{VariableTimestep{TIMES}, T_data, 2}, idx::AnyIndex, ts::TimestepValue{T_time}) where {T_data, TIMES, T_time}
 	t = _get_time_value_position(TIMES, ts)
-	mat.data isa SubArray ? view_offset = mat.data.indices[2][1] + 1 : view_offset = 0
+	mat.data isa SubArray ? view_offset = mat.data.indices[2][1] - 1 : view_offset = 0
 	t = t - view_offset	
 	data = mat.data[idx, t]
 	_missing_data_check(data, t)
@@ -306,28 +306,28 @@ end
 
 function Base.setindex!(mat::TimestepMatrix{FixedTimestep{FIRST, STEP, LAST}, T_data, 1}, val, ts::TimestepValue{T_time}, idx::AnyIndex) where {T_data, FIRST, STEP, LAST, T_time}
 	t = _get_time_value_position([FIRST:STEP:LAST...], ts)
-	mat.data isa SubArray ? view_offset = mat.data.indices[1][1] + 1 : view_offset = 0
+	mat.data isa SubArray ? view_offset = mat.data.indices[1][1] - 1 : view_offset = 0
 	t = t - view_offset
 	setindex!(mat.data, val, t, idx)
 end
 
 function Base.setindex!(mat::TimestepMatrix{VariableTimestep{TIMES}, T_data, 1}, val, ts::TimestepValue{T_time}, idx::AnyIndex) where {T_data, TIMES, T_time}
 	t = _get_time_value_position(TIMES, ts)
-	mat.data isa SubArray ? view_offset = mat.data.indices[1][1] + 1 : view_offset = 0
+	mat.data isa SubArray ? view_offset = mat.data.indices[1][1] - 1 : view_offset = 0
 	t = t - view_offset
 	setindex!(mat.data, val, t, idx)
 end
 
 function Base.setindex!(mat::TimestepMatrix{FixedTimestep{FIRST, STEP, LAST}, T_data, 2}, val, idx::AnyIndex, ts::TimestepValue{T_time}) where {T_data, FIRST, STEP, LAST, T_time}
 	t = _get_time_value_position([FIRST:STEP:LAST...], ts)
-	mat.data isa SubArray ? view_offset = mat.data.indices[2][1] + 1 : view_offset = 0
+	mat.data isa SubArray ? view_offset = mat.data.indices[2][1] - 1 : view_offset = 0
 	t = t - view_offset
 	setindex!(mat.data, val, idx, t)
 end
 
 function Base.setindex!(mat::TimestepMatrix{VariableTimestep{TIMES}, T_data, 2}, val, idx::AnyIndex, ts::TimestepValue{T_time}) where {T_data, TIMES, T_time}
 	t = _get_time_value_position(TIMES, ts)
-	mat.data isa SubArray ? view_offset = mat.data.indices[2][1] + 1 : view_offset = 0
+	mat.data isa SubArray ? view_offset = mat.data.indices[2][1] - 1 : view_offset = 0
 	t = t - view_offset
 	setindex!(mat.data, val, idx, t)
 end
@@ -397,7 +397,7 @@ function Base.getindex(arr::TimestepArray{FixedTimestep{FIRST, STEP, LAST}, T_da
 	_single_index_check(arr.data, idxs)
 	idxs1, ts, idxs2 = split_indices(idxs, ti)
 	t = _get_time_value_position([FIRST:STEP:LAST...], ts)
-	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] + 1 : view_offset = 0
+	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] - 1 : view_offset = 0
 	t = t - view_offset
 	return arr.data[idxs1..., t, idxs2...]
 end
@@ -406,7 +406,7 @@ function Base.getindex(arr::TimestepArray{VariableTimestep{TIMES}, T_data, N, ti
 	_single_index_check(arr.data, idxs)
 	idxs1, ts, idxs2 = split_indices(idxs, ti)
 	t = _get_time_value_position(TIMES, ts)
-	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] + 1 : view_offset = 0
+	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] - 1 : view_offset = 0
 	t = t - view_offset
 	return arr.data[idxs1..., t, idxs2...]
 end
@@ -441,7 +441,7 @@ function Base.setindex!(arr::TimestepArray{FixedTimestep{FIRST, STEP, LAST}, T_d
 	_single_index_check(arr.data, idxs)
 	idxs1, ts, idxs2 = split_indices(idxs, ti)
 	t = _get_time_value_position([FIRST:STEP:LAST...], ts)
-	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] + 1 : view_offset = 0
+	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] - 1 : view_offset = 0
 	t = t - view_offset
 	setindex!(arr.data, val, idxs1..., t, idxs2...)
 end
@@ -450,7 +450,7 @@ function Base.setindex!(arr::TimestepArray{VariableTimestep{TIMES}, T_data, N, t
 	_single_index_check(arr.data, idxs)
 	idxs1, ts, idxs2 = split_indices(idxs, ti)
 	t = _get_time_value_position(TIMES, ts)
-	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] + 1 : view_offset = 0
+	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] - 1 : view_offset = 0
 	t = t - view_offset
 	setindex!(arr.data, val, idxs1..., t, idxs2...)
 end
@@ -475,7 +475,7 @@ end
 function Base.getindex(arr::TimestepArray{FixedTimestep{FIRST, STEP, LAST}, T_data, N, ti}, idxs::Union{Array{TimestepValue{T_time},1}, AnyIndex}...) where {T_data, N, ti, FIRST, STEP, LAST, T_time}
 	idxs1, ts_array, idxs2 = split_indices(idxs, ti)
 	ts_idxs = _get_ts_indices(ts_array, [FIRST:STEP:LAST...])
-	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] + 1 : view_offset = 0
+	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] - 1 : view_offset = 0
 	ts_idxs = ts_idxs .- view_offset
 	return arr.data[idxs1..., ts_idxs, idxs2...]
 end
@@ -483,7 +483,7 @@ end
 function Base.getindex(arr::TimestepArray{VariableTimestep{TIMES}, T_data, N, ti}, idxs::Union{Array{TimestepValue{T_time},1}, AnyIndex}...) where {T_data, N, ti, TIMES, T_time}
 	idxs1, ts_array, idxs2 = split_indices(idxs, ti)
 	ts_idxs = _get_ts_indices(ts_array, TIMES)
-	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] + 1 : view_offset = 0
+	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] - 1 : view_offset = 0
 	ts_idxs = ts_idxs .- view_offset
 	return arr.data[idxs1..., ts_idxs, idxs2...]
 end
@@ -497,7 +497,7 @@ end
 function Base.setindex!(arr::TimestepArray{FixedTimestep{FIRST, STEP, LAST}, T_data, N, ti}, vals, idxs::Union{Array{TimestepValue{T_time},1}, AnyIndex}...) where {T_data, N, ti, FIRST, STEP, LAST, T_time}
 	idxs1, ts_array, idxs2 = split_indices(idxs, ti)
 	ts_idxs = _get_ts_indices(ts_array, [FIRST:STEP:LAST...])
-	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] + 1 : view_offset = 0
+	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] - 1 : view_offset = 0
 	ts_idxs = ts_idxs .- view_offset
 	setindex!(arr.data, vals, idxs1..., ts_idxs, idxs2...)
 end
@@ -505,7 +505,7 @@ end
 function Base.setindex!(arr::TimestepArray{VariableTimestep{TIMES}, T_data, N, ti}, vals, idxs::Union{Array{TimestepValue{T_time},1}, AnyIndex}...) where {T_data, N, ti, TIMES, T_time}
 	idxs1, ts_array, idxs2 = split_indices(idxs, ti)
 	ts_idxs = _get_ts_indices(ts_array, TIMES)
-	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] + 1 : view_offset = 0
+	arr.data isa SubArray ? view_offset = arr.data.indices[ti][1] - 1 : view_offset = 0
 	ts_idxs = ts_idxs .- view_offset
 	setindex!(arr.data, vals, idxs1..., ts_idxs, idxs2...)
 end
diff --git a/test/test_timesteparrays.jl b/test/test_timesteparrays.jl
index d3162a759..80c0b5e59 100644
--- a/test/test_timesteparrays.jl
+++ b/test/test_timesteparrays.jl
@@ -745,3 +745,34 @@ reset_time_val(x, zeros(10))
 reset_time_val(y, collect(reshape(zeros(8), 4, 2)))
 
 end #module
+
+#------------------------------------------------------------------------------
+# 8. Test handling of offsets for TimestepValue and TimestepIndex with a TimestepMatrix
+#   --> this is a very specific test to handle PR #857, specifically for methods
+#       using offset - 1 in time.jl
+#------------------------------------------------------------------------------
+
+@defcomp testcomp begin
+
+    var_tvalue = Variable(index=[time, regions])
+    var_tindex = Variable(index=[time, regions])
+
+    function run_timestep(p, v, d, t)
+        for r in d.regions
+            tvalue = TimestepValue(2003)
+            tindex = TimestepIndex(1)
+
+            v.var_tvalue[tvalue,r] = 999
+            v.var_tindex[tindex,r] = 999
+        end
+    end
+end
+
+m = Model()
+set_dimension!(m, :time, 2000:2005)
+set_dimension!(m, :regions, ["A", "B"])
+add_comp!(m, testcomp, first = 2003)
+run(m)
+
+@test m[:testcomp, :var_tvalue][findfirst(i -> i == 2003, 2000:2005), :] == [999., 999.]
+@test m[:testcomp, :var_tindex][findfirst(i -> i == 2003, 2000:2005), :] == [999., 999.]