diff --git a/library/md4.c b/library/md4.c
index 156e715..41c5d54 100644
--- a/library/md4.c
+++ b/library/md4.c
@@ -148,8 +148,8 @@
 #define P(a,b,c,d,x,s)         \
     do                         \
     {                          \
-        (a) += F(b,c,d) + (x); \
-        (a) = S(a,s);          \
+        (a) += F((b),(c),(d)) + (x);             \
+        (a) = S((a),(s));                        \
     } while( 0 )