diff --git a/lib/register/instructions/get_slot.rb b/lib/register/instructions/get_slot.rb
index 0206418f..d2e3fda1 100644
--- a/lib/register/instructions/get_slot.rb
+++ b/lib/register/instructions/get_slot.rb
@@ -22,6 +22,9 @@ module Register
       @register = register
       @array = array
       @index = index
+      raise "not integer #{index}" unless index.is_a? Numeric
+      raise "Not register #{register}" unless Register::RegisterReference.look_like_reg(register)
+      raise "Not register #{array}" unless Register::RegisterReference.look_like_reg(array)
     end
     attr_accessor :register , :array , :index
   end
diff --git a/lib/register/instructions/set_slot.rb b/lib/register/instructions/set_slot.rb
index ac0a80ab..ef191210 100644
--- a/lib/register/instructions/set_slot.rb
+++ b/lib/register/instructions/set_slot.rb
@@ -16,11 +16,14 @@ module Register
 
     # If you had a c array and index offset
     # the instruction would do array[index] = register
-    # So SGetSlot means the register (first argument) moves to the slot (array and index)
+    # So SetSlot means the register (first argument) moves to the slot (array and index)
     def initialize register , array , index
       @register = register
       @array = array
       @index = index
+      raise "not integer #{index}" unless index.is_a? Numeric
+      raise "Not register #{register}" unless Register::RegisterReference.look_like_reg(register)
+      raise "Not register #{array}" unless Register::RegisterReference.look_like_reg(array)
     end
     attr_accessor :register , :array , :index
   end