diff --git a/src/MachO/MachOFat.jl b/src/MachO/MachOFat.jl
index b636f21..52f83e1 100644
--- a/src/MachO/MachOFat.jl
+++ b/src/MachO/MachOFat.jl
@@ -11,8 +11,8 @@ abstract type MachOFatArchitecture end
 end
 
 @io struct MachOFatArch64 <: MachOFatArchitecture
-    cputype::UInt64
-    cpusubtype::UInt64
+    cputype::UInt32
+    cpusubtype::UInt32
     offset::UInt64
     size::UInt64
     align::UInt32
@@ -59,7 +59,7 @@ function readmeta(io::IO,::Type{FatMachOHandle})
 
     # Unpack the header
     header = unpack(io, header_type, endianness)
-    return FatMachOHandle(io, start, header, path(io))
+    return FatMachOHandle(io, Int64(start), header, path(io))
 end
 
 # Iteration
@@ -67,7 +67,7 @@ keys(h::FatMachOHandle) = 1:length(h)
 iterate(h::FatMachOHandle, idx=1) = idx > length(h) ? nothing : (h[idx], idx+1)
 lastindex(h::FatMachOHandle) = lastindex(h.header.archs)
 length(h::FatMachOHandle) = length(h.header.archs)
-eltype(::Type{S}) where {S <: FatMachOHandle} = MachOLoadCmdRef
+eltype(::Type{<:FatMachOHandle}) = MachOHandle
 function getindex(h::FatMachOHandle, idx)
     seek(h.io, h.start + h.header.archs[idx].offset)
     only(readmeta(h.io, MachOHandle))
diff --git a/src/MachO/MachOHeader.jl b/src/MachO/MachOHeader.jl
index de965e6..9a855e4 100644
--- a/src/MachO/MachOHeader.jl
+++ b/src/MachO/MachOHeader.jl
@@ -74,9 +74,9 @@ Given the `magic` field from a Mach-O file header, return the endianness of the
 Mach-O header.
 """
 function macho_endianness(magic::UInt32)
-    if magic in (MH_CIGAM, MH_CIGAM_64, FAT_CIGAM, FAT_CIGAM_METAL)
+    if magic in (MH_CIGAM, MH_CIGAM_64, FAT_CIGAM, FAT_CIGAM_64, FAT_CIGAM_METAL)
         return :BigEndian
-    elseif magic in (MH_MAGIC, MH_MAGIC_64, FAT_MAGIC, FAT_MAGIC_METAL, METALLIB_MAGIC)
+    elseif magic in (MH_MAGIC, MH_MAGIC_64, FAT_MAGIC, FAT_MAGIC_64, FAT_MAGIC_METAL, METALLIB_MAGIC)
         return :LittleEndian
     else
         throw(MagicMismatch("Invalid Magic (0x$(string(magic, base=16, pad=8)))!"))
diff --git a/test/mac64/libfoo_fat64.dylib b/test/mac64/libfoo_fat64.dylib
new file mode 100755
index 0000000..09a0549
Binary files /dev/null and b/test/mac64/libfoo_fat64.dylib differ
diff --git a/test/runtests.jl b/test/runtests.jl
index c5b1146..860620e 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -207,7 +207,7 @@ function test_libfoo_and_fooifier(fooifier_path, libfoo_path)
 end
 
 function test_fat_libfoo(file)
-    ohs = readmeta(open(file, "r"))
+    ohs = readmeta(file isa IO ? file : open(file, "r"))
     @test isa(ohs, FatMachOHandle)
     @test length(ohs) == 2
     ntotal, n64 = 0, 0
@@ -217,6 +217,10 @@ function test_fat_libfoo(file)
     end
     @test ntotal == 2
     @test n64 == 1
+
+    handles = collect(ohs)
+    @test handles isa Vector{<:MachOHandle}
+    @test length(handles) == 2
 end
 
 function test_metal(file)
@@ -241,6 +245,9 @@ test_libfoo_and_fooifier("./linux64/fooifier", "./linux64/libfoo.so")
 # Run MachO tests
 test_libfoo_and_fooifier("./mac64/fooifier", "./mac64/libfoo.dylib")
 test_fat_libfoo("./mac64/libfoo_fat.dylib")
+test_fat_libfoo(IOBuffer(read("./mac64/libfoo_fat.dylib")))
+test_fat_libfoo("./mac64/libfoo_fat64.dylib")
+test_fat_libfoo(IOBuffer(read("./mac64/libfoo_fat64.dylib")))
 test_metal("./macmetal/dummy")
 
 # Run COFF tests