diff --git a/Project.toml b/Project.toml
index 27a3bd0..8183fb2 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "MRCFile"
 uuid = "c18c01d3-0ab9-49c3-bd2d-8f2e64a2b7a5"
 authors = ["Seth Axen <seth@sethaxen.com>"]
-version = "0.1.0"
+version = "0.1.1"
 
 [deps]
 CodecBzip2 = "523fee87-0ab8-5b00-afb7-3ecf72e48cfd"
diff --git a/src/data.jl b/src/data.jl
index d75ddec..c9f72cf 100644
--- a/src/data.jl
+++ b/src/data.jl
@@ -90,7 +90,7 @@ function updateheader!(d::MRCData; statistics=true)
 
     # misc
     h.mode = TYPE_TO_MODE[eltype(d)]
-    h.nsymbt = bytesize(extendedheader(d))
+    h.nsymbt = sizeof(extendedheader(d))
     h.nlabl = sum(s -> length(rstrip(s)) > 0, h.label)
 
     # update statistics
diff --git a/test/data.jl b/test/data.jl
new file mode 100644
index 0000000..2125b06
--- /dev/null
+++ b/test/data.jl
@@ -0,0 +1,132 @@
+@testset "MRCData" begin
+    @testset "MRCData(header, extendedheader, data)" begin
+        h = MRCHeader()
+        exh = MRCExtendedHeader()
+        data = Array{Float32,3}(undef, (2, 2, 2))
+        d = MRCData(h, exh, data)
+        @test d.header === h
+        @test d.extendedheader === exh
+        @test d.data === data
+        @test eltype(d) === Float32
+        @test ndims(d) === 3
+    end
+
+    @testset "MRCData(header, extendedheader)" begin
+        h = MRCHeader()
+        exh = MRCExtendedHeader()
+        d = MRCData(h, exh)
+        @test d.header === h
+        @test d.extendedheader === exh
+        @test ndims(d) == ndims(h)
+        @test size(d) == size(h)
+    end
+
+    @testset "MRCData(size::NTuple{3,<:Integer})" begin
+        d = MRCData((10, 20, 30))
+        @test size(d) == (10, 20, 30)
+        @test size(d.data) == (10, 20, 30)
+        @test ndims(d) == 3
+        @test ndims(d.data) == 3
+
+        @testset "header(d::MRCData)" begin
+            h = header(d)
+            @test h.nx == 10
+            @test h.ny == 20
+            @test h.nz == 30
+        end
+    end
+
+    @testset "MRCData(size::Integer...)" begin
+        d1 = MRCData(10, 20, 30)
+        d2 = MRCData((10, 20, 30))
+        @test size(d1) == size(d2)
+    end
+
+    data = fill(1.0f0, (2, 2, 2))
+    h = MRCHeader()
+    exh = MRCExtendedHeader()
+    d = MRCData(h, exh, data)
+
+    @testset "getindex" begin
+        @test d[1, 1, 1] == 1.0f0
+        @test d[2, 1, 1] == 1.0f0
+        @test d[1, 2, 1] == 1.0f0
+        @test d[2, 2, 1] == 1.0f0
+        @test d[1, 1, 2] == 1.0f0
+        @test d[2, 1, 2] == 1.0f0
+        @test d[1, 2, 2] == 1.0f0
+        @test d[2, 2, 2] == 1.0f0
+    end
+
+    @testset "setindex!" begin
+        d[1, 1, 1] = 10
+        d[2, 1, 1] = 20
+        d[1, 2, 1] = 30
+        d[2, 2, 1] = 40
+        d[1, 1, 2] = 50
+        d[2, 1, 2] = 60
+        d[1, 2, 2] = 70
+        d[2, 2, 2] = 80
+        @test d[1, 1, 1] == 10
+        @test d[2, 1, 1] == 20
+        @test d[1, 2, 1] == 30
+        @test d[2, 2, 1] == 40
+        @test d[1, 1, 2] == 50
+        @test d[2, 1, 2] == 60
+        @test d[1, 2, 2] == 70
+        @test d[2, 2, 2] == 80
+    end
+
+    @testset "size" begin
+        @test size(d) == (2, 2, 2)
+        @test size(d, 1) == 2
+        @test size(d, 2) == 2
+        @test size(d, 3) == 2
+    end
+
+    @testset "ndims" begin
+        @test ndims(d) == 3
+    end
+
+    @testset "length" begin
+        @test length(d) == 8
+    end
+
+    @testset "iterate" begin
+        iter = iterate(d)
+        @test iter !== nothing && first(iter) == 10
+    end
+
+    @testset "lastindex" begin
+        @test lastindex(d) == 8
+    end
+
+    @testset "similar" begin
+        d_similar = similar(d)
+        @test typeof(d_similar) === typeof(d)
+        @test size(d_similar) == size(d)
+        @test eltype(d_similar) == eltype(d)
+    end
+
+    @testset "IndexStyle" begin
+        @test Base.IndexStyle(typeof(d)) == Base.IndexStyle(typeof(d.data))
+    end
+end
+
+@testset "updateheader!(d::MRCData; statistics=true)" begin
+    data = fill(1.0f0, (2, 2, 2))
+    h = MRCHeader()
+    @test h.nx == 0
+    @test h.ny == 0
+    @test h.nz == 0
+    exh = MRCExtendedHeader()
+    d = MRCData(h, exh, data)
+    updateheader!(d)
+    @test d.header.dmin == 1.0f0
+    @test d.header.dmax == 1.0f0
+    @test d.header.dmean == 1.0f0
+    @test d.header.rms == 0.0f0
+    @test d.header.nx == 2
+    @test d.header.ny == 2
+    @test d.header.nz == 2
+end
diff --git a/test/runtests.jl b/test/runtests.jl
index 0feedc6..2fdd44d 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -5,4 +5,5 @@ using Test
     include("utils.jl")
     include("header.jl")
     include("io.jl")
+    include("data.jl")
 end