diff --git a/src/hence/emulator.cr b/src/hence/emulator.cr
index 5fa5a4e..003797c 100644
--- a/src/hence/emulator.cr
+++ b/src/hence/emulator.cr
@@ -184,13 +184,13 @@ module Hence
         when 0x08 # shr
           @reg_tmp = @reg_a >> @reg_b
         when 0x09 # add
-          @reg_tmp = @reg_a &+ @reg_b &+ (@reg_s & 0b00000001_u8)
+          @reg_tmp = @reg_a &+ @reg_b
           @reg_s &= 0b11111110_u8
           if @reg_tmp < @reg_a
             @reg_s |= 0b00000001_u8
           end
         when 0x0a # sub
-          @reg_tmp = @reg_a &- @reg_b &- (@reg_s & 0b00000001_u8)
+          @reg_tmp = @reg_a &- @reg_b
           @reg_s &= 0b11111110_u8
           if @reg_tmp > @reg_a
             @reg_s |= 0b00000001_u8
diff --git a/src/hence/firmware/firmwares/default.yml b/src/hence/firmware/firmwares/default.yml
index 51d1cf0..7652970 100644
--- a/src/hence/firmware/firmwares/default.yml
+++ b/src/hence/firmware/firmwares/default.yml
@@ -104,20 +104,6 @@ sections:
           tmpl 0xb
           alu 0x01
           push
-      - name: clc
-        description: Clears carry flag
-        opcode: null
-        arg: null
-        stack:
-          input: []
-          output: []
-        microcode: |
-          tmpsr 0xd
-          tmpl 0xa
-          tmps 0b11111110
-          tmpl 0xb
-          alu 0x01
-          tmpl 0xd
   - name: stack-manipulation
     description: Stack manipulation
     opcodes: