diff --git a/xpcom/io/nsLocalFileCommon.cpp b/xpcom/io/nsLocalFileCommon.cpp
index 32f855dd8e5..3002046c8b5 100644
--- a/xpcom/io/nsLocalFileCommon.cpp
+++ b/xpcom/io/nsLocalFileCommon.cpp
@@ -1,4 +1,4 @@
-/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
 /* ***** BEGIN LICENSE BLOCK *****
  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
  *
@@ -45,6 +45,8 @@
 #include "nsReadableUtils.h"
 #include "nsPrintfCString.h"
 #include "nsCRT.h"
+#include "nsNativeCharsetUtils.h"
+#include "nsUTF8Utils.h"
 
 #ifdef XP_WIN
 #include <string.h>
@@ -77,40 +79,91 @@ nsLocalFile::InitWithFile(nsILocalFile *aFile)
 
 #define kMaxFilenameLength 255
 #define kMaxExtensionLength 100
-// requirement: kMaxExtensionLength < kMaxFilenameLength - 4
+#define kMaxSequenceNumberLength 5 // "-9999"
+// requirement: kMaxExtensionLength < kMaxFilenameLength - kMaxSequenceNumberLength
 
 NS_IMETHODIMP
 nsLocalFile::CreateUnique(PRUint32 type, PRUint32 attributes)
 {
-    nsresult rv = Create(type, attributes);
-    if (rv != NS_ERROR_FILE_ALREADY_EXISTS)
+    nsresult rv;
+    PRBool longName;
+
+#ifdef XP_WIN
+    nsAutoString pathName, leafName, rootName, suffix;
+    rv = GetPath(pathName);
+#else
+    nsCAutoString pathName, leafName, rootName, suffix; 
+    rv = GetNativePath(pathName);
+#endif
+    if (NS_FAILED(rv))
         return rv;
 
-    nsCAutoString leafName; 
+    longName = (pathName.Length() + kMaxSequenceNumberLength >
+                kMaxFilenameLength);
+    if (!longName)
+    {
+        rv = Create(type, attributes);
+        if (rv != NS_ERROR_FILE_ALREADY_EXISTS)
+            return rv;
+    }
+
+#ifdef XP_WIN
+    rv = GetLeafName(leafName);
+    if (NS_FAILED(rv))
+        return rv;
+
+    const PRInt32 lastDot = leafName.RFindChar(PRUnichar('.'));
+#else
     rv = GetNativeLeafName(leafName);
     if (NS_FAILED(rv))
         return rv;
 
-    const char* lastDot = strrchr(leafName.get(), '.');
-    char suffix[kMaxExtensionLength] = "";
-    if (lastDot)
+    const PRInt32 lastDot = leafName.RFindChar('.');
+#endif
+
+    if (lastDot == kNotFound)
     {
-        PL_strncpyz(suffix, lastDot, sizeof(suffix)); // include '.'
-        leafName.SetLength(lastDot - leafName.get()); // strip suffix and dot.
+        rootName = leafName;
+    } 
+    else
+    {
+        suffix = Substring(leafName, lastDot);      // include '.'
+        rootName = Substring(leafName, 0, lastDot); // strip suffix and dot
     }
 
-    PRUint32 maxRootLength = (kMaxFilenameLength - 4) - strlen(suffix) - 1;
-
-    if (leafName.Length() > maxRootLength)
-        leafName.SetLength(maxRootLength);
+    if (longName)
+    {
+        PRUint32 maxRootLength = (kMaxFilenameLength -
+                                  (pathName.Length() - leafName.Length()) -
+                                  suffix.Length() - kMaxSequenceNumberLength);
+#ifdef XP_WIN
+        // ensure that we don't cut the name in mid-UTF16-character
+        rootName.SetLength(NS_IS_LOW_SURROGATE(rootName[maxRootLength]) ?
+                           maxRootLength - 1 : maxRootLength);
+        SetLeafName(rootName + suffix);
+#else
+        if (NS_IsNativeUTF8())
+            // ensure that we don't cut the name in mid-UTF8-character
+            while (UTF8traits::isInSeq(rootName[maxRootLength]))
+                --maxRootLength;
+        rootName.SetLength(maxRootLength);
+        SetNativeLeafName(rootName + suffix);
+#endif
+        nsresult rv = Create(type, attributes);
+        if (rv != NS_ERROR_FILE_ALREADY_EXISTS)
+            return rv;
+    }
 
     for (int indx = 1; indx < 10000; indx++)
     {
         // start with "Picture-1.jpg" after "Picture.jpg" exists
-        SetNativeLeafName(leafName +
-                          nsPrintfCString("-%d", indx) +
-                          nsDependentCString(suffix));
-
+#ifdef XP_WIN
+        SetLeafName(rootName +
+                    NS_ConvertASCIItoUTF16(nsPrintfCString("-%d", indx)) +
+                    suffix);
+#else
+        SetNativeLeafName(rootName + nsPrintfCString("-%d", indx) + suffix);
+#endif
         rv = Create(type, attributes);
         if (NS_SUCCEEDED(rv) || rv != NS_ERROR_FILE_ALREADY_EXISTS) 
             return rv;
diff --git a/xpcom/tests/unit/test_bug364285-1.js b/xpcom/tests/unit/test_bug364285-1.js
new file mode 100644
index 00000000000..347fcfe81c6
--- /dev/null
+++ b/xpcom/tests/unit/test_bug364285-1.js
@@ -0,0 +1,51 @@
+const Ci = Components.interfaces;
+const Cc = Components.classes;
+
+var nameArray = [
+ "ascii",                                           // ASCII
+ "fran\u00E7ais",                                   // Latin-1
+ "\u0420\u0443\u0441\u0441\u043A\u0438\u0439",      // Cyrillic
+ "\u65E5\u672C\u8A9E",                              // Japanese
+ "\u4E2D\u6587",                                    // Chinese
+ "\uD55C\uAD6D\uC5B4",                              // Korean
+ "\uD801\uDC0F\uD801\uDC2D\uD801\uDC3B\uD801\uDC2B" // Deseret
+];
+
+function getTempDir()
+{
+    var dirService = Cc["@mozilla.org/file/directory_service;1"]
+	.getService(Ci.nsIProperties);
+    return dirService.get("TmpD", Ci.nsILocalFile);
+}
+
+function create_file(fileName)
+{
+    var outFile = getTempDir();
+    outFile.append(fileName);
+    outFile.createUnique(outFile.NORMAL_FILE_TYPE, 0600);
+
+    var stream = Cc["@mozilla.org/network/file-output-stream;1"]
+	.createInstance(Ci.nsIFileOutputStream);
+    stream.init(outFile, 0x02 | 0x08 | 0x20, 0600, 0);
+    stream.write("foo", 3);
+    stream.close();
+
+    do_check_eq(outFile.leafName.substr(0, fileName.length), fileName);
+
+    return outFile;
+}
+
+function test_create(fileName)
+{
+    var file1 = create_file(fileName);
+    var file2 = create_file(fileName);
+    file1.remove(false);
+    file2.remove(false);
+}
+
+function run_test()
+{
+    for (var i = 0; i < nameArray.length; ++i) {
+	test_create(nameArray[i]);
+    }
+}