diff --git a/src/simulator/register.rs b/src/simulator/register.rs
index d352d74..4cbe50d 100644
--- a/src/simulator/register.rs
+++ b/src/simulator/register.rs
@@ -22,7 +22,7 @@ impl<U: RegisterNum> Register<U> {
 
 	/// Set value of register *position* to *value* 
 	pub fn set_reg(&mut self, position: usize, value: U) {
-		self.register[position] = value;
+		if position != 0 { self.register[position] = value; }
 	}