diff --git a/src/ieu/bmu/bmuctrl.sv b/src/ieu/bmu/bmuctrl.sv
index b45a13ff3..ef021db0e 100644
--- a/src/ieu/bmu/bmuctrl.sv
+++ b/src/ieu/bmu/bmuctrl.sv
@@ -121,8 +121,16 @@ module bmuctrl(
                                else 
                                  BMUControlsD = `BMUCTRLW'b000_0100_000;  // count instruction
       17'b0011011_0110000_001:   BMUControlsD = `BMUCTRLW'b000_0100_000;  // count word instruction
+      17'b0111011_0000100_100: if (`XLEN == 64)
+                                 BMUControlsD = `BMUCTRLW'b000_0100_100;  // zexth (rv64)
+                               else 
+                                 BMUControlsD = `BMUCTRLW'b000_0000_000;  // illegal instruction
+      17'b0110011_0000100_100: if (`XLEN == 32)
+                                 BMUControlsD = `BMUCTRLW'b000_0100_100;  // zexth (rv32)
+                               else 
+                                 BMUControlsD = `BMUCTRLW'b000_0000_000;  // illegal instruction
                                  
-      default:                   BMUControlsD = {Funct3D, {7'b0}};    // not B instruction or shift
+      default:                   BMUControlsD = {Funct3D, {7'b0}};        // not B instruction or shift
     endcase
 
   // Unpack Control Signals
diff --git a/src/ieu/bmu/ext.sv b/src/ieu/bmu/ext.sv
index c9f845e76..05cb24c01 100644
--- a/src/ieu/bmu/ext.sv
+++ b/src/ieu/bmu/ext.sv
@@ -31,13 +31,21 @@
 `include "wally-config.vh"
 
 module ext #(parameter WIDTH = 32) (
-  input  logic [WIDTH-1:0] A,            // Operand
-  output logic [WIDTH-1:0] sexthResult,  // sign extend halfword result
-  output logic [WIDTH-1:0] sextbResult,  // sign extend byte result
-  output logic [WIDTH-1:0] zexthResult); // zero extend halfword result 
+  input  logic [WIDTH-1:0] A, B,         // Operands
+  output logic [WIDTH-1:0] ExtResult);   // Extend Result
 
+  logic [WIDTH-1:0] sexthResult, zexthResult, sextbResult;
   assign sexthResult = {{(WIDTH-16){A[15]}},A[15:0]};
   assign zexthResult = {{(WIDTH-16){1'b0}},A[15:0]};
   assign sextbResult = {{(WIDTH-8){A[7]}},A[7:0]};
+
+  always_comb 
+    case({B[2],B[0]})
+      2'b00: ExtResult = zexthResult;
+      2'b10: ExtResult = sextbResult;
+      2'b11: ExtResult = sexthResult;
+      default: ExtResult = 0;
+    endcase
+
  
 endmodule
\ No newline at end of file
diff --git a/src/ieu/bmu/zbb.sv b/src/ieu/bmu/zbb.sv
index 1be801f4b..d5198d484 100644
--- a/src/ieu/bmu/zbb.sv
+++ b/src/ieu/bmu/zbb.sv
@@ -47,19 +47,18 @@ module zbb #(parameter WIDTH=32) (
   logic [WIDTH-1:0] Rev8Result;
 
   // sign/zero extend results
-  logic [WIDTH-1:0] sexthResult;         // sign extend halfword result
-  logic [WIDTH-1:0] sextbResult;         // sign extend byte result
-  logic [WIDTH-1:0] zexthResult;         // zero extend halfword result 
+  logic [WIDTH-1:0] ExtResult;           // sign/zero extend result
 
   cnt #(WIDTH) cnt(.A(A), .B(B), .W64(W64), .CntResult(CntResult));
   byteUnit #(WIDTH) bu(.A(A), .OrcBResult(OrcBResult), .Rev8Result(Rev8Result));
-  ext #(WIDTH) ext(.A(A), .sexthResult(sexthResult), .sextbResult(sextbResult), .zexthResult(zexthResult));
+  ext #(WIDTH) ext(.A(A), .B(B), .ExtResult(ExtResult));
 
   //can replace with structural mux by looking at bit 4 in rs2 field
   always_comb begin 
       case (ZBBSelect)
       3'b111: ZBBResult = ALUResult;  // rotate
       3'b000: ZBBResult = CntResult;  // count
+      3'b100: ZBBResult = ExtResult;  // sign/zero extend
       /*15'b0010100_101_00111: ZBBResult = OrcBResult;
       15'b0110100_101_11000: ZBBResult = Rev8Result;
       15'b0110101_101_11000: ZBBResult = Rev8Result;