diff --git a/bits/22_xmlutils.js b/bits/22_xmlutils.js
index fb4e5ef..3318fb3 100644
--- a/bits/22_xmlutils.js
+++ b/bits/22_xmlutils.js
@@ -153,7 +153,13 @@ function utf8readb(data) {
 function utf8readc(data) { return Buffer_from(data, 'binary').toString('utf8'); }
 
 var utf8corpus = "foo bar baz\u00e2\u0098\u0083\u00f0\u009f\u008d\u00a3";
-var utf8read = has_buf && (/*#__PURE__*/utf8readc(utf8corpus) == /*#__PURE__*/utf8reada(utf8corpus) && utf8readc || /*#__PURE__*/utf8readb(utf8corpus) == /*#__PURE__*/utf8reada(utf8corpus) && utf8readb) || utf8reada;
+var utf8read = /*#__PURE__*/(function() {
+  if(has_buf) {
+    if(utf8readc(utf8corpus) == utf8reada(utf8corpus)) return utf8readc;
+    if(utf8readb(utf8corpus) == utf8reada(utf8corpus)) return utf8readb;
+  }
+  return utf8reada;
+})();
 
 var utf8write/*:StringConv*/ = has_buf ? function(data) { return Buffer_from(data, 'utf8').toString("binary"); } : function(orig/*:string*/)/*:string*/ {
 	var out/*:Array<string>*/ = [], i = 0, c = 0, d = 0;
diff --git a/bits/88_write.js b/bits/88_write.js
index 7ca6a42..076856a 100644
--- a/bits/88_write.js
+++ b/bits/88_write.js
@@ -111,7 +111,7 @@ function write_binary_type(out, opts/*:WriteOpts*/)/*:any*/ {
 
 function writeSyncXLSX(wb/*:Workbook*/, opts/*:?WriteOpts*/) {
 	reset_cp();
-	check_wb(wb);
+	if(!opts || !opts.unsafe) check_wb(wb);
 	var o = dup(opts||{});
 	if(o.cellStyles) { o.cellNF = true; o.sheetStubs = true; }
 	if(o.type == "array") { o.type = "binary"; var out/*:string*/ = (writeSyncXLSX(wb, o)/*:any*/); o.type = "array"; return s2ab(out); }
@@ -120,7 +120,7 @@ function writeSyncXLSX(wb/*:Workbook*/, opts/*:?WriteOpts*/) {
 
 function writeSync(wb/*:Workbook*/, opts/*:?WriteOpts*/) {
 	reset_cp();
-	check_wb(wb);
+	if(!opts || !opts.unsafe) check_wb(wb);
 	var o = dup(opts||{});
 	if(o.cellStyles) { o.cellNF = true; o.sheetStubs = true; }
 	if(o.type == "array") { o.type = "binary"; var out/*:string*/ = (writeSync(wb, o)/*:any*/); o.type = "array"; return s2ab(out); }
diff --git a/types/index.d.ts b/types/index.d.ts
index 5d1811f..c75f4ae 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -317,6 +317,9 @@ export interface WritingOptions extends CommonOptions {
 
     /** Record Separator ("row separator") for CSV / Text output */
     RS?: string;
+
+    /** Skip certain validity checks (NOTE: generated files may not open in Excel) */
+    unsafe?: boolean;
 }
 
 /** Workbook Object */