diff --git a/src/ocpu/ocpu.c b/src/ocpu/ocpu.c
index 064c997..9d05e93 100644
--- a/src/ocpu/ocpu.c
+++ b/src/ocpu/ocpu.c
@@ -572,6 +572,86 @@ void ocpu_execute() {
 	ocpu.F++;
 	break;
 	
+      default:
+	printf("Wrong register: %02X\n", reg);
+	return;
+      }
+      break;
+    case INS_DEC:
+      reg = ocpu_fetch_byte();
+      switch(reg) {
+      case REG_AL:
+	ocpu.A--;
+	ocpu.AL = ocpu.A & 0xFF;
+	break;
+      case REG_AH:
+	ocpu.A--;
+	ocpu.AH = ocpu.A >> 8;
+	break;
+      case REG_A:
+	ocpu.A--;
+	break;
+	
+      case REG_BL:
+	ocpu.B--;
+	ocpu.BL = ocpu.B & 0xFF;
+	break;
+      case REG_BH:
+	ocpu.B--;
+	ocpu.BH = ocpu.B >> 8;
+	break;
+      case REG_B:
+	ocpu.B--;
+	break;
+	
+      case REG_CL:
+        ocpu.C--;
+	ocpu.CL = ocpu.C & 0xFF;
+	break;
+      case REG_CH:
+	ocpu.C--;
+	ocpu.CH = ocpu.C >> 8;
+	break;
+      case REG_C:
+	ocpu.C--;
+	break;
+	
+      case REG_DL:
+	ocpu.D--;
+	ocpu.DL = ocpu.D & 0xFF;
+	break;
+      case REG_DH:
+	ocpu.D--;
+	ocpu.DH = ocpu.D >> 8;
+	break;
+      case REG_D:
+	ocpu.D--;
+	break;
+
+      case REG_EL:
+        ocpu.E--;
+	ocpu.EL = ocpu.E & 0xFF;
+	break;
+      case REG_EH:
+	ocpu.E--;
+	ocpu.EH = ocpu.E >> 8;
+	break;
+      case REG_E:
+	ocpu.E--;
+	break;
+
+      case REG_FL:
+        ocpu.F--;
+	ocpu.FL = ocpu.F & 0xFF;
+	break;
+      case REG_FH:
+	ocpu.F--;
+	ocpu.FH = ocpu.F >> 8;
+	break;
+      case REG_F:
+	ocpu.F--;
+	break;
+	
       default:
 	printf("Wrong register: %02X\n", reg);
 	return;
diff --git a/src/ocpu/ocpu.h b/src/ocpu/ocpu.h
index 9aad35a..05909a6 100644
--- a/src/ocpu/ocpu.h
+++ b/src/ocpu/ocpu.h
@@ -36,6 +36,7 @@
 #define INS_ADD_IM 0x10
 #define INS_ADD_REG 0xB0
 #define INS_INC 0x15
+#define INS_DEC 0x16
 
 struct OCPU_MEMORY {
   byte memory[MAX_MEMORY];