diff --git a/gas/config/tc-avr.c b/gas/config/tc-avr.c
index 8f6d0ec..6e6f0d0 100644
--- a/gas/config/tc-avr.c
+++ b/gas/config/tc-avr.c
@@ -862,28 +862,40 @@ avr_operand (struct avr_opcodes_s *opcode,
     case 'r':
     case 'a':
     case 'v':
-      if (*str == 'r' || *str == 'R')
-        {
-          char r_name[20];
-
-          str = extract_word (str, r_name, sizeof (r_name));
-          op_mask = 0xff;
-          if (ISDIGIT (r_name[1]))
-            {
-              if (r_name[2] == '\0')
-                op_mask = r_name[1] - '0';
-              else if (r_name[1] != '0'
-                       && ISDIGIT (r_name[2])
-                       && r_name[3] == '\0')
-                op_mask = (r_name[1] - '0') * 10 + r_name[2] - '0';
-            }
-        }
-      else
-        {
-          op_mask = avr_get_constant (str, 31);
-          str = input_line_pointer;
-        }
-
+      {
+        char * old_str = str;
+        char *lower;
+        char r_name[20];
+        
+        str = extract_word (str, r_name, sizeof (r_name));
+        for (lower = r_name; *lower; ++lower)
+ 	      {
+	        if (*lower >= 'A' && *lower <= 'Z')
+	          *lower += 'a' - 'A';
+          }
+        if (r_name[0] == 'r' && ISDIGIT (r_name[1]) && r_name[2] == 0)
+          /* Single-digit register number, ie r0-r9 */
+          op_mask = r_name[1] - '0';
+        else if (r_name[0] == 'r' && ISDIGIT (r_name[1]) &&
+          ISDIGIT (r_name[2]) && r_name[3] == 0)
+          /* Double-digit register number, ie r10 - r32 */
+          op_mask = (r_name[1] - '0') * 10 + r_name[2] - '0';
+        else if (r_name[0] >= 'x' && r_name[0] <= 'z' &&
+          (r_name[1] == 'l' || r_name[1] == 'h') && r_name[2] == 0)
+          /* registers r26-r31 referred to by name, ie xl, xh, yl, yh, zl, zh */
+          op_mask = (r_name[0] - 'x') * 2 + (r_name[1] == 'h') + 26;
+        else if ((*op == 'v' || *op == 'w') &&
+          r_name[0] >= 'x' && r_name[0] <= 'z' && r_name[1] == 0)
+          /* For the movw and addiw instructions, refer to registers x, y and z by name */
+          op_mask = (r_name[0] - 'x') * 2 + 26;
+        else
+          {
+            /* Numeric or symbolic constant register number */
+            op_mask = avr_get_constant (old_str, 31);
+            str = input_line_pointer;
+          }
+       }
+ 	  
       if (avr_mcu->isa & AVR_ISA_FEW_REGS)
         {
           if (op_mask < 16 || op_mask >= 32)