diff --git a/ARMeilleure/Decoders/OpCode32AluBf.cs b/ARMeilleure/Decoders/OpCode32AluBf.cs
index 00794d7907..1e7bea7473 100644
--- a/ARMeilleure/Decoders/OpCode32AluBf.cs
+++ b/ARMeilleure/Decoders/OpCode32AluBf.cs
@@ -22,7 +22,7 @@ namespace ARMeilleure.Decoders
             Rn = (opCode >> 0) & 0xf;
 
             Msb = ((opCode >> 16) & 31);
-            Lsb = ((opCode >> 17) & 31);
+            Lsb = Msb - ((opCode >> 10) & 31);
         }
     }
 }
diff --git a/ARMeilleure/Decoders/OpCodeTable.cs b/ARMeilleure/Decoders/OpCodeTable.cs
index c650fac635..ad99b33e7a 100644
--- a/ARMeilleure/Decoders/OpCodeTable.cs
+++ b/ARMeilleure/Decoders/OpCodeTable.cs
@@ -616,6 +616,7 @@ namespace ARMeilleure.Decoders
             SetA32("<<<<000100101111111111110011xxxx", InstName.Blx,   InstEmit32.Blxr,  typeof(OpCode32BReg));
             SetA32("<<<<000100101111111111110001xxxx", InstName.Bx,    InstEmit32.Bx,    typeof(OpCode32BReg));
             SetT32("xxxxxxxxxxxxxxxx010001110xxxx000", InstName.Bx,    InstEmit32.Bx,    typeof(OpCodeT16BReg));
+            SetA32("<<<<000101101111xxxx11110001xxxx", InstName.Clz,   InstEmit32.Clz,   typeof(OpCode32AluReg));
             SetA32("<<<<00110101xxxx0000xxxxxxxxxxxx", InstName.Cmp,   InstEmit32.Cmp,   typeof(OpCode32AluImm));
             SetA32("<<<<00010101xxxx0000xxxxxxx0xxxx", InstName.Cmp,   InstEmit32.Cmp,   typeof(OpCode32AluRsImm));
             //RsReg missing
diff --git a/ARMeilleure/Instructions/InstEmitAlu32.cs b/ARMeilleure/Instructions/InstEmitAlu32.cs
index 00c15c1ffb..4bd8c124e0 100644
--- a/ARMeilleure/Instructions/InstEmitAlu32.cs
+++ b/ARMeilleure/Instructions/InstEmitAlu32.cs
@@ -31,6 +31,16 @@ namespace ARMeilleure.Instructions
             EmitAluStore(context, res);
         }
 
+        public static void Clz(ArmEmitterContext context)
+        {
+            IOpCode32AluReg op = (IOpCode32AluReg)context.CurrOp;
+
+            Operand m = GetAluM(context, setCarry: false);
+
+            Operand res = context.CountLeadingZeros(m);
+            EmitAluStore(context, res);
+        }
+
         public static void Cmp(ArmEmitterContext context)
         {
             IOpCode32Alu op = (IOpCode32Alu)context.CurrOp;
@@ -282,7 +292,7 @@ namespace ARMeilleure.Instructions
             OpCode32AluBf op = (OpCode32AluBf)context.CurrOp;
 
             Operand d = GetIntOrZR(context, op.Rd);
-            Operand res = context.BitwiseAnd(d, Const(~op.SourceMask));
+            Operand res = context.BitwiseAnd(d, Const(~op.DestMask));
 
             SetIntA32(context, op.Rd, res);
         }
@@ -294,7 +304,8 @@ namespace ARMeilleure.Instructions
             Operand n = GetIntOrZR(context, op.Rn);
             Operand d = GetIntOrZR(context, op.Rd);
             Operand part = context.BitwiseAnd(n, Const(op.SourceMask));
-            Operand res = context.BitwiseAnd(d, Const(~op.SourceMask));
+            if (op.Lsb != 0) part = context.ShiftLeft(part, Const(op.Lsb));
+            Operand res = context.BitwiseAnd(d, Const(~op.DestMask));
             res = context.BitwiseOr(res, part);
 
             SetIntA32(context, op.Rd, res);