diff --git a/src/global.h b/src/global.h
index 138e11a..d3d015c 100644
--- a/src/global.h
+++ b/src/global.h
@@ -11,6 +11,8 @@
 
 // Number of General Purpose Registers.
 #define REGISTER_COUNT 31
+// Register identifier interpreted as the 'zero register'
+#define ZERO_REGISTER 31
 // Size of the memory in bytes.
 #define MEMORY_SIZE 2097152
 // Length of the memory address in bits.