diff --git a/out.sh b/out.sh
index 8c723a7..e2ac63b 100755
--- a/out.sh
+++ b/out.sh
@@ -2,7 +2,7 @@
 set -o errexit -o pipefail
 export LC_ALL=C
 rootfiles=(s js big_favicon.png favicon.ico css.css tiles.png help.png index.html index_multifile.xhtml)
-jsfiles=(cc.js dict_editor.js structures.js obj_editor.js cselect.js guimgr.js main_gui.js console_helpers.js)
+jsfiles=(cc.js utf8to16.js dict_editor.js structures.js obj_editor.js cselect.js guimgr.js main_gui.js console_helpers.js)
 
 d=$(dirname -- "$0")
 cd -- "$d"
diff --git a/src/css.css b/src/css.css
index ef4e1ba..f489790 100644
--- a/src/css.css
+++ b/src/css.css
@@ -620,12 +620,14 @@ hr{
 .growc>*{
 	flex-grow:1;
 }
-a.thiccb{
-	padding:10px;
+a.btn{
 	color:var(--Link);
 	text-decoration:underline;
 	white-space:pre-wrap;
 }
+a.thiccb{
+	padding:10px;
+}
 input.thiccb{
 	padding:10px;
 	text-align:left;
diff --git a/src/index_multifile.xhtml b/src/index_multifile.xhtml
index 688c778..d9b035a 100644
--- a/src/index_multifile.xhtml
+++ b/src/index_multifile.xhtml
@@ -17,6 +17,7 @@
 <link rel='stylesheet' href='css.css'/>
 <script src='js/inlineables.js'></script>
 <script src='js/cc.js'></script>
+<script src='js/utf8to16.js'></script>
 <script src='js/dict_editor.js'></script>
 <script src='js/structures.js'></script>
 <script src='js/obj_editor.js'></script>
diff --git a/src/js/cc.js b/src/js/cc.js
index b1f7969..f221d47 100644
--- a/src/js/cc.js
+++ b/src/js/cc.js
@@ -262,13 +262,24 @@ function cc_load_gzip_file_reader_onload(){
 		ch=str.writable.getWriter();
 		ch.write(cc);
 		ch.close();
-		ch=str.readable.pipeThrough(new TextDecoderStream('utf-8',{'fatal':true})).getReader();
-		str='';
+		ch=str.readable.getReader();
+		cc=[];
 		ch.read().then(function ondata(d){
-			if(d.done)cc_load_xml_string(str);
-			else try{
-				str+=d.value;
-				ch.read().then(ondata,pos);
+			try{
+				if(d.done){
+					if(cc.length===1)buf=cc[0];
+					else{
+						var i=cc.length,j=0,buf;
+						while(i)j+=cc[--i].length;
+						buf=new Uint8Array(j);
+						i=cc.length;
+						while(i)buf.set(cc[--i],j-=cc[i].length);
+					}
+					utf8to16(cc_load_xml_string,loading_modal_abort,buf,'',0);
+				}else{
+					cc.push(d.value);
+					ch.read().then(ondata,pos);
+				}
 			}catch(error){
 				pos(error);
 			}
@@ -279,13 +290,11 @@ function cc_load_gzip_file_reader_onload(){
 }
 
 function cc_load_xml_file_reader_onload(){
-	try{
-		var s=decodeURIComponent(escape(this.result));
-	}catch(error){
-		say_error('bad UTF-8',error);
-		return;
-	}
-	cc_load_xml_string(s);
+	utf8to16(cc_load_xml_string,loading_modal_abort,new Uint8Array(this.result),'',0);
+}
+
+function loading_modal_abort(){
+	current_gui().error_tag.textContent='bad UTF-8 (aborted)';
 }
 
 function cc_load_gzip(file){
@@ -361,10 +370,7 @@ function cc_load_aes_file_reader_onload(){
 			if(!decryptedbuf)throw Error('padding = 0');
 			var m=i---decryptedbuf;
 			while(i>m)if(decryptedbuf!==decrypted[--i])throw Error('padding bytes not all equal');
-			cc_load_xml_string(new TextDecoder('utf-8',{
-				'fatal':true,
-				'ignoreBOM':false
-			}).decode(decrypted.subarray(0,m)));
+			utf8to16(cc_load_xml_string,loading_modal_abort,decrypted.subarray(0,m),'',0);
 		}).catch(say_error.bind(null,'AES-ECB 256 decrypt'));
 	}catch(error){
 		say_error('AES-ECB 256 decrypt',error);
@@ -443,7 +449,7 @@ function cc_load_xml(file){
 		var fr=new FileReader();
 		fr.addEventListener('error',file_reader_onerror,onceel);
 		fr.addEventListener('load',cc_load_xml_file_reader_onload,onceel);
-		fr.readAsBinaryString(file);
+		fr.readAsArrayBuffer(file);
 	}catch(error){
 		say_error('FileReader',error);
 	}
diff --git a/src/js/dict_editor.js b/src/js/dict_editor.js
index 1c2138b..4efa0d4 100644
--- a/src/js/dict_editor.js
+++ b/src/js/dict_editor.js
@@ -216,10 +216,10 @@ function xml_ie_back(){
 
 function xml_ie_show_error(e){
 	console.error(e);
-	var li=cre('li'),g=current_gui();
+	var li=cre('li');
 	li.style.backgroundColor='var(--Bad)';
 	li.textContent=e;
-	g.status.appendChild(li);
+	current_gui().status.appendChild(li);
 	set_loading(false);
 }
 
@@ -228,13 +228,10 @@ function xml_ie_filereader_onerror(){
 }
 
 function xml_ie_filereader_onload(){
-	try{
-		var g=decodeURIComponent(escape(this.result));
-	}catch(error){
-		xml_ie_show_error('bad UTF-8');
-		console.error('original error:',error);
-		return;
-	}
+	utf8to16(xml_ie_utf8to16_callback,xml_ie_utf8to16_abort,new Uint8Array(this.result),'',0);
+}
+
+function xml_ie_utf8to16_callback(g){
 	try{
 		var d=document.implementation.createDocument(null,'d',null).documentElement;
 		d.innerHTML=g;
@@ -250,6 +247,13 @@ function xml_ie_filereader_onload(){
 	}
 }
 
+function xml_ie_utf8to16_abort(){
+	var li=cre('li');
+	li.style.backgroundColor='var(--Bad)';
+	li.textContent='bad UTF-8 (aborted)';
+	current_gui().status.appendChild(li);
+}
+
 function xml_ie_import(){
 	var g=current_gui(),f=g.last_blob_url;
 	if(f){
@@ -270,7 +274,7 @@ function xml_ie_import(){
 		g=new FileReader();
 		g.addEventListener('error',xml_ie_filereader_onerror,onceel);
 		g.addEventListener('load',xml_ie_filereader_onload,onceel);
-		g.readAsBinaryString(f);
+		g.readAsArrayBuffer(f);
 	}catch(error){
 		xml_ie_show_error(error);
 	}
diff --git a/src/js/guimgr.js b/src/js/guimgr.js
index 81c88ed..dc93d93 100644
--- a/src/js/guimgr.js
+++ b/src/js/guimgr.js
@@ -449,15 +449,13 @@ function AdvFileLoader(raw,out){
 AdvFileLoader.prototype.handleEvent=function(e){
 	switch(e.type){
 		case 'load':
-			if(this.raw)e=e.target.result;
-			else try{
-				e=decodeURIComponent(escape(e.target.result));
-			}catch(error){
-				say_error('bad UTF-8',error);
+			if(this.raw){
+				this.out.setvalchg(e.target.result);
+				set_loading(false);
 				return;
 			}
-			this.out.setvalchg(e);
-			set_loading(false);
+			var r=this.out;
+			utf8to16(AdvFileLoader.utf8to16_callback.bind(this.out),Function.prototype,new Uint8Array(e.target.result),'',0);
 			return;
 		case 'error':
 			say_error('FileReader',e.target.error);
@@ -466,13 +464,18 @@ AdvFileLoader.prototype.handleEvent=function(e){
 			if(e=e.target.files[0]){
 				set_loading(true);
 				try{
-					var r=new FileReader();
+					r=new FileReader();
 					r.addEventListener('load',this,onceel);
 					r.addEventListener('error',this,onceel);
-					r.readAsBinaryString(e);
+					r[this.raw?'readAsBinaryString':'readAsArrayBuffer'](e);
 				}catch(error){
 					say_error('FileReader',error);
 				}
 			}
 	}
+};
+
+AdvFileLoader.utf8to16_callback=function(str){
+	this.setvalchg(str);
+	set_loading(false);
 };
\ No newline at end of file
diff --git a/src/js/utf8to16.js b/src/js/utf8to16.js
new file mode 100644
index 0000000..98200ee
--- /dev/null
+++ b/src/js/utf8to16.js
@@ -0,0 +1,86 @@
+'use strict';
+
+//https://encoding.spec.whatwg.org/#utf-8-decoder
+
+function utf8to16(callback_ok,callback_abort,buf,outstr,i){
+	var l=buf.length,chr=String.fromCharCode,b1,b2,b3,b4,j;
+	oof:do{
+		for(;i!==l;++i){
+			if(buf[j=i]<128){
+				if((b1=l-i)>8192)b1=8192;
+				while(++i,--b1&&buf[i]<128);
+				outstr+=chr.apply(null,buf.subarray(j,i--));
+				continue;
+			}
+			if((b1=buf[i])<194||b1>244
+				||++i===l)continue oof;
+			b2=buf[i];
+			//b1 is valid start of multi-byte code point
+			if(b1<224){
+				//110xxxxx (2 byte code point)
+				if(b2<128||b2>191)continue oof;
+				outstr+=chr(b2^(b1<<6)^12416);
+				continue;
+			}
+			if(b1<240){
+				//1110xxxx (3 byte code point)
+				if(b2<(b1===224?160:128)||b2>(b1===237?159:191)
+					||++i===l
+					||(b3=buf[i])<128||b3>191)continue oof;
+				outstr+=chr(b3^(b2<<6)^(b1<<12)^925824);
+				continue;
+			}
+			//11110xxx (4 byte code point)
+			if(b2<(b1===240?144:128)||b2>(b1===244?143:191)
+				||++i===l
+				||(b3=buf[i])<128||b3>191
+				||++i===l
+				||(b4=buf[i])<128||b4>191)continue oof;
+			outstr+=chr(
+				(b3>>4)+(b2<<2)+(b1<<8)-6728,
+				b4^((b3&15)<<6)^56448
+			);
+		}
+		callback_ok(outstr);
+		return;
+	}while(!callback_abort&&(i+=i===j,outstr+='\uFFFD'));
+
+	//ask how to handle error
+	//don't set tbl.innerHTML because browser adds <tbody> in html mode (non-xhtml)
+	var tbl=cre('table'),tr=cre('tr');
+	tbl.className='tableborder';
+	tr.innerHTML='<th colspan="2" style="background-color:var(--Bad);">bad UTF-8</th>';
+	tbl.appendChild(tr);
+	(tr=cre('tr')).innerHTML='<td>code point offset inside data:</td><td>'+j+'</td>';
+	tbl.appendChild(tr);
+	(tr=cre('tr')).innerHTML='<td>error offset inside code point:</td><td>'+(i-j)+'</td>';
+	tbl.appendChild(tr);
+	(tr=cre('tr')).innerHTML='<td>data length:</td><td>'+l+'</td>';
+	tbl.appendChild(tr);
+	(tr=cre('tr')).innerHTML='<td colspan="2"><input value="abort" data-a="a" type="button"/><input value="replace errors" title="replace errors with U+FFFD like str(data,&apos;utf-8&apos;,&apos;replace&apos;) in python3" data-a="r" type="button"/><a data-a="s" download="bad_utf8.bin" href="javascript:;" class="btn" style="display:inline-block;">save data</a></td>';
+	tr.firstChild.addEventListener('click',function(e){
+		switch((e=e.target).dataset.a){
+			case 'a':
+				pop_gui();
+				callback_abort();
+				set_loading(false);
+				return;
+			case 'r':
+				set_loading(true);
+				pop_gui();
+				utf8to16(callback_ok,null,buf,outstr+'\uFFFD',i+(i===j));
+				return;
+			case 's':
+				setTimeout(revoke_href,0,e);
+				e.href=URL.createObjectURL(new Blob([buf],binblobopts));
+		}
+	},capel);
+	tbl.appendChild(tr);
+	push_gui(tbl,true);
+	set_loading(false);
+}
+
+function revoke_href(a){
+	URL.revokeObjectURL(a.href);
+	a.href='javascript:;';
+}
\ No newline at end of file