diff --git a/include/lib/zt_common.h b/include/lib/zt_common.h
index cb8e30e2..437a2915 100644
--- a/include/lib/zt_common.h
+++ b/include/lib/zt_common.h
@@ -21,11 +21,13 @@
  * Usage example:
  *  #define IMAGE_ENTRY _AC(0x10000, UL)
  */
+#ifndef _AC
 #ifdef __ASSEMBLER__
 #define _AC(X, TYPE)	X
 #else
 #define _AC(X, TYPE)	X##TYPE
 #endif
+#endif
 
 
 #ifndef __ASSEMBLER__