diff --git a/gas/config/tc-aarch64.h b/gas/config/tc-aarch64.h
index df73516022f..7a9a4e77bff 100644
--- a/gas/config/tc-aarch64.h
+++ b/gas/config/tc-aarch64.h
@@ -191,7 +191,10 @@ struct aarch64_frag_type
       goto LABEL;								\
     }
 
+/* COFF sub section alignment calculated using the write.c implementation.  */
+#ifndef OBJ_COFF
 #define SUB_SEGMENT_ALIGN(SEG, FRCHAIN) 0
+#endif
 
 #define DWARF2_LINE_MIN_INSN_LENGTH 	4