diff --git a/data/customXml.xlsx b/data/customXml.xlsx
new file mode 100644
index 0000000..d8a8362
Binary files /dev/null and b/data/customXml.xlsx differ
diff --git a/src/read.jl b/src/read.jl
index c938715..9973a82 100644
--- a/src/read.jl
+++ b/src/read.jl
@@ -203,7 +203,10 @@ function open_or_read_xlsx(source::Union{IO, AbstractString}, read_files::Bool,
                 continue
             end
 
-            if endswith(f.name, ".xml") || endswith(f.name, ".rels")
+            # Rather than ignore custom XML internal files here, let them get passed through to write like binaries are.
+            if !startswith(f.name, "customXml") && (endswith(f.name, ".xml") || endswith(f.name, ".rels"))
+            #if endswith(f.name, ".xml") || endswith(f.name, ".rels")
+                
                 # XML file
                 internal_xml_file_add!(xf, f.name)
                 if read_files
@@ -215,9 +218,10 @@ function open_or_read_xlsx(source::Union{IO, AbstractString}, read_files::Bool,
                     end
 
                     # ignore custom XML internal files
-                    if startswith(f.name, "customXml")
-                        continue
-                    end
+                    # no longer needed if these files are passed through like binary files
+                    #if startswith(f.name, "customXml")
+                    #    continue
+                    #end
 
                     internal_xml_file_read(xf, f.name)
                 end
@@ -225,6 +229,7 @@ function open_or_read_xlsx(source::Union{IO, AbstractString}, read_files::Bool,
 
                 # Binary file
                 # we only read binary files to save the Excel file later
+                # Custom XML files also now get passed through this way, too
                 bytes = ZipFile.read(f)
                 @assert sizeof(bytes) == f.uncompressedsize
                 xf.binary_data[f.name] = bytes
diff --git a/test/runtests.jl b/test/runtests.jl
index 84f762f..85eeb00 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1113,6 +1113,31 @@ end
     isfile(filename_copy) && rm(filename_copy)
 end
 
+@testset "CustomXml" begin
+    # issue #210
+    # None of the example .xlsx files in the test suite include custoimXml internal files
+    # but customXml.xlsx does
+    template = XLSX.open_xlsx_template(joinpath(data_directory, "customXml.xlsx")) 
+    filename_copy = "customXml_copy.xlsx"
+    for sn in XLSX.sheetnames(template)
+        sheet = template[sn]
+        sheet["Q1"] = "Cant" # using an apostrophe here causes a test failure reading the copy - "Evaluated: "Can't" == "Can't""
+        sheet["Q2"] = "write"
+        sheet["Q3"] = "this"
+        sheet["Q4"] = "template"
+    end
+    @test XLSX.writexlsx(filename_copy, template, overwrite=true) == nothing # This is where the bug will throw if custoimXml internal files present.
+    @test isfile(filename_copy)
+    f_copy = XLSX.readxlsx(filename_copy) # Don't really think this second part is necessary.
+    test_Xmlread = [["Cant", "write", "this", "template"]]
+    for sn in XLSX.sheetnames(f_copy)
+        sheet = template[sn]
+        data = [[sheet["Q1"], sheet["Q2"], sheet["Q3"], sheet["Q4"]]]
+        check_test_data(data, test_Xmlread)
+    end
+    isfile(filename_copy) && rm(filename_copy)
+end
+
 @testset "Edit Template" begin
     new_filename = "new_file_from_empty_template.xlsx"
     f = XLSX.open_empty_template()