diff --git a/src/hence/emulator.cr b/src/hence/emulator.cr
index 003797c..5fa5a4e 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_tmp = @reg_a &+ @reg_b &+ (@reg_s & 0b00000001_u8)
           @reg_s &= 0b11111110_u8
           if @reg_tmp < @reg_a
             @reg_s |= 0b00000001_u8
           end
         when 0x0a # sub
-          @reg_tmp = @reg_a &- @reg_b
+          @reg_tmp = @reg_a &- @reg_b &- (@reg_s & 0b00000001_u8)
           @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 7652970..51d1cf0 100644
--- a/src/hence/firmware/firmwares/default.yml
+++ b/src/hence/firmware/firmwares/default.yml
@@ -104,6 +104,20 @@ 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: