diff --git a/src/a64instruction_global.h b/src/a64instruction_global.h
index 421a838..489fe06 100644
--- a/src/a64instruction_global.h
+++ b/src/a64instruction_global.h
@@ -1,4 +1,14 @@
+#ifndef __A64INSTRUCTION_GLOBAL__
+#define __A64INSTRUCTION_GLOBAL__
 #include <stdint.h>
 
 // Specifies the register being referred to
 typedef uint8_t a64inst_regSpecifier;
+
+// Denotes the type of register being referred to
+typedef enum {
+    a64inst_W = 0,
+    a64inst_R = 1
+} a64inst_regType;
+
+#endif