diff --git a/src/memline.c b/src/memline.c
index 9c15fa7..e1a4cb3 100644
--- a/src/memline.c
+++ b/src/memline.c
@@ -227,7 +227,7 @@
 #define ML_INSERT	0x12	    // insert line
 #define ML_FIND		0x13	    // just find the line
 #define ML_FLUSH	0x02	    // flush locked block
-#define ML_SIMPLE(x)	(x & 0x10)  // DEL, INS or FIND
+#define ML_SIMPLE(x)	((x) & 0x10)  // DEL, INS or FIND
 
 // argument for ml_upd_block0()
 typedef enum {