diff --git a/src/common/strbuf.h b/src/common/strbuf.h
index f1493240d..7592e2e12 100644
--- a/src/common/strbuf.h
+++ b/src/common/strbuf.h
@@ -141,7 +141,7 @@ INLINE void SB_SetIndex (StrBuf* B, unsigned Index)
     B->Index = Index;
 }
 #else
-#  define SB_SetIndex(B)  ((B)->Index = (Index))
+#  define SB_SetIndex(B, Index) ((B)->Index = (Index))
 #endif
 
 #if defined(HAVE_INLINE)