diff --git a/opcodes/B[ab]x.v b/opcodes/B[ab]x.v
index b2e92e5..5eabcdf 100644
--- a/opcodes/B[ab]x.v
+++ b/opcodes/B[ab]x.v
@@ -30,4 +30,8 @@
     next_cycle <= `BUSCMD_NOP;
     decstate <= `DEC_ALU_INIT;
     alu_return <= `DEC_START;
+
+`ifdef SIM
+
+`endif
 end
\ No newline at end of file
diff --git a/opcodes/z_alu_phase_3.v b/opcodes/z_alu_phase_3.v
index 1f0a1fa..2bd0029 100644
--- a/opcodes/z_alu_phase_3.v
+++ b/opcodes/z_alu_phase_3.v
@@ -22,28 +22,41 @@
         `ALU_REG_B: B[alu_first*4+:4] <= 0;
         `ALU_REG_C: C[alu_first*4+:4] <= 0;
         `ALU_REG_D: D[alu_first*4+:4] <= 0;
-        default: $display("ALU_OP_ZERO register not handled");
+        default: begin
+            $display("ALU_OP_ZERO register not handled");
+            alu_requested_halt <= 1;
+        end
         endcase
         alu_first <= (alu_first + 1) & 4'hF;
     end
     `ALU_OP_2CMPL: begin
         case (alu_reg_dest)
         `ALU_REG_A: {Carry, A[alu_first*4+:4]} <= !alu_src1 + alu_carry;
-        default: $display("ALU_OP_2CMPL register not handled");
+        default: begin
+            $display("ALU_OP_2CMPL register not handled");
+            alu_requested_halt <= 1;
+        end
         endcase
         alu_first <= (alu_first + 1) & 4'hF;
     end
     `ALU_OP_1CMPL: begin
         case (alu_reg_dest)
         `ALU_REG_A: A[alu_first*4+:4] <= ~alu_src1;
-        default: $display("ALU_OP_1CMPL register not handled");
+        `ALU_REG_C: C[alu_first*4+:4] <= ~alu_src1;
+        default: begin
+            $display("ALU_OP_1CMPL register not handled");
+            alu_requested_halt <= 1;
+        end
         endcase
         alu_first <= (alu_first + 1) & 4'hF;
     end
     `ALU_OP_INC: begin
         case (alu_reg_dest)
         `ALU_REG_D: {Carry, D[alu_first*4+:4]} <= alu_src1 + alu_carry;
-        default: $display("ALU_OP_INC register not handled");
+        default: begin
+            $display("ALU_OP_INC register not handled");
+            alu_requested_halt <= 1;
+        end
         endcase
         alu_first <= (alu_first + 1) & 4'hF;
     end