diff --git a/src/crab/arm/arm.cr b/src/crab/arm/arm.cr
index cd714ca..90f0ae8 100644
--- a/src/crab/arm/arm.cr
+++ b/src/crab/arm/arm.cr
@@ -69,7 +69,7 @@ module ARM
     puts "Unused instruction: #{hex_str instr}"
   end
 
-  def rotate_register(instr : Word, carry_out : Pointer(Bool), allow_register_shifts = true) : Word
+  def rotate_register(instr : Word, carry_out : Pointer(Bool), allow_register_shifts : Bool) : Word
     reg = bits(instr, 0..3)
     shift_type = bits(instr, 5..6)
     if allow_register_shifts && bit?(instr, 4)
diff --git a/src/crab/arm/data_processing.cr b/src/crab/arm/data_processing.cr
index ee4ac6d..8c1eabe 100644
--- a/src/crab/arm/data_processing.cr
+++ b/src/crab/arm/data_processing.cr
@@ -14,7 +14,7 @@ module ARM
     operand_2 = if imm_flag # Operand 2 is an immediate
                   immediate_offset bits(instr, 0..11), pointerof(barrel_shifter_carry_out)
                 else # Operand 2 is a register
-                  rotate_register bits(instr, 0..11), pointerof(barrel_shifter_carry_out)
+                  rotate_register bits(instr, 0..11), pointerof(barrel_shifter_carry_out), allow_register_shifts: true
                 end
     case opcode
     when 0b0000 # AND