diff --git a/src/avrdude.conf.in b/src/avrdude.conf.in
index 4b4135e1..f874d40b 100644
--- a/src/avrdude.conf.in
+++ b/src/avrdude.conf.in
@@ -6237,6 +6237,7 @@ part parent "m324p" # m324pb
     memory "sernum"
         size               = 10;
         offset             = 0xe; # Sub-region of prodsig
+        read               = "0 0 1 1 a0 0 0 0  0 0 0 0 0 0 0 0  0 0 0 0 a4 a3 a2 a1  o o o o o o o o";
     ;
 ;
 
@@ -11045,6 +11046,7 @@ part parent "m328" # m328pb
     memory "sernum"
         size               = 10;
         offset             = 0xe; # Sub-region of prodsig
+        read               = "0 0 1 1 a0 0 0 0  0 0 0 0 0 0 0 0  0 0 0 0 a4 a3 a2 a1  o o o o o o o o";
     ;
 ;
 
@@ -20451,7 +20453,7 @@ part parent ".reduced_core_tiny" # t102
 
     memory "sernum"
         size               = 10;
-        offset             = 0x6; # Sub-region of prodsig
+        offset             = 0x3fc6; # Sub-region of prodsig
     ;
 
     memory "io"
@@ -20499,7 +20501,7 @@ part parent ".reduced_core_tiny" # t104
 
     memory "sernum"
         size               = 10;
-        offset             = 0x6; # Sub-region of prodsig
+        offset             = 0x3fc6; # Sub-region of prodsig
     ;
 
     memory "io"
diff --git a/src/config_gram.y b/src/config_gram.y
index 11e57316..62f0e673 100644
--- a/src/config_gram.y
+++ b/src/config_gram.y
@@ -374,7 +374,7 @@ part_def :
 
         m->type &= and_mask;
         // Remove MEM_IN_SIGROW attribute from classic calibration and classic/XMEGA signature mem
-        if(!(current_part->prog_modes & (PM_PDI|PM_UPDI))) {
+        if(current_part->prog_modes & PM_Classic) {
           if(mem_is_signature(m))
             m->type &= ~MEM_IN_SIGROW;
           if(mem_is_calibration(m))
@@ -1396,11 +1396,11 @@ static int parse_cmdbits(OPCODE * op, int opnum)
         case 'a':
           sb = opnum == AVR_OP_LOAD_EXT_ADDR? bitno+8: bitno-8; // should be this number
           if(bitno < 8 || bitno > 23) {
-            if(!current_mem || !mem_is_sigrow(current_mem)) // Known exemption
+            if(!current_mem || !mem_is_in_sigrow(current_mem)) // Known exemptions
               yywarning("address bits don't normally appear in Bytes 0 or 3 of SPI commands");
           } else if((bn & 31) != sb) {
             if(!current_part || !str_casestarts(current_part->desc, "AT89S5")) // Exempt AT89S5x
-              if(!current_mem || !mem_is_sigrow(current_mem)) // and prodsig
+              if(!current_mem || !mem_is_in_sigrow(current_mem)) // ... and prodsig/sernum
                 yywarning("a%d would normally be expected to be a%d", bn, sb);
           } else if(bn < 0 || bn > 31)
             yywarning("invalid address bit a%d, using a%d", bn, bn & 31);