Index: firmware/drivers/fat.c
===================================================================
--- firmware/drivers/fat.c	(revision 13496)
+++ firmware/drivers/fat.c	(working copy)
@@ -1172,13 +1172,44 @@
     
     return 0;
 }
-
+static bool is_char_legal(char c)
+{
+    switch(c)
+    {
+        case 0x22:
+        case 0x2a:
+        case 0x2b:
+        case 0x2c:
+        case 0x2e:
+        case 0x3a:
+        case 0x3b:
+        case 0x3c:
+        case 0x3d:
+        case 0x3e:
+        case 0x3f:
+        case 0x5b:
+        case 0x5c:
+        case 0x5d:
+        case 0x7c:
+            return false;
+        default:
+            if(c <= 0x20)
+                return false;
+    }
+    return true;
+}
 static int fat_checkname(const unsigned char* newname)
 {
     /* More sanity checks are probably needed */
     if ( newname[strlen(newname) - 1] == '.' ) {
         return -1;
     }
+    while (*newname)
+    {
+        if (!is_char_legal(*newname))
+            return -1;
+        newname++;
+    }
     return 0;
 }
 
@@ -1346,35 +1377,19 @@
 
 static unsigned char char2dos(unsigned char c, int* randomize)
 {
-    switch(c)
+    if (!is_char_legal(c))
     {
-        case 0x22:
-        case 0x2a:
-        case 0x2b:
-        case 0x2c:
-        case 0x2e:
-        case 0x3a:
-        case 0x3b:
-        case 0x3c:
-        case 0x3d:
-        case 0x3e:
-        case 0x3f:
-        case 0x5b:
-        case 0x5c:
-        case 0x5d:
-        case 0x7c:
+        if(c <= 0x20)
+            c = 0;   /* Illegal char, remove */
+        else
+        {
             /* Illegal char, replace */
             c = '_';
             *randomize = 1; /* as per FAT spec */
-            break;
-                
-        default:
-            if(c <= 0x20)
-                c = 0;   /* Illegal char, remove */
-            else
-                c = toupper(c);
-            break;
+        }
     }
+    else
+        c = toupper(c);
     return c;
 }