diff --git a/library/md4.c b/library/md4.c
index 3f8ddff..156e715 100644
--- a/library/md4.c
+++ b/library/md4.c
@@ -137,15 +137,21 @@
     GET_UINT32_LE( X[14], data, 56 );
     GET_UINT32_LE( X[15], data, 60 );
 
-#define S(x,n) ((x << n) | ((x & 0xFFFFFFFF) >> (32 - n)))
+#define S(x,n) (((x) << (n)) | (((x) & 0xFFFFFFFF) >> (32 - (n))))
 
     A = ctx->state[0];
     B = ctx->state[1];
     C = ctx->state[2];
     D = ctx->state[3];
 
-#define F(x, y, z) ((x & y) | ((~x) & z))
-#define P(a,b,c,d,x,s) { a += F(b,c,d) + x; a = S(a,s); }
+#define F(x, y, z) (((x) & (y)) | ((~(x)) & (z)))
+#define P(a,b,c,d,x,s)         \
+    do                         \
+    {                          \
+        (a) += F(b,c,d) + (x); \
+        (a) = S(a,s);          \
+    } while( 0 )
+
 
     P( A, B, C, D, X[ 0],  3 );
     P( D, A, B, C, X[ 1],  7 );
@@ -167,8 +173,13 @@
 #undef P
 #undef F
 
-#define F(x,y,z) ((x & y) | (x & z) | (y & z))
-#define P(a,b,c,d,x,s) { a += F(b,c,d) + x + 0x5A827999; a = S(a,s); }
+#define F(x,y,z) (((x) & (y)) | ((x) & (z)) | ((y) & (z)))
+#define P(a,b,c,d,x,s)                          \
+    do                                          \
+    {                                           \
+        (a) += F(b,c,d) + (x) + 0x5A827999;     \
+        (a) = S(a,s);                           \
+    } while( 0 )
 
     P( A, B, C, D, X[ 0],  3 );
     P( D, A, B, C, X[ 4],  5 );
@@ -190,8 +201,13 @@
 #undef P
 #undef F
 
-#define F(x,y,z) (x ^ y ^ z)
-#define P(a,b,c,d,x,s) { a += F(b,c,d) + x + 0x6ED9EBA1; a = S(a,s); }
+#define F(x,y,z) ((x) ^ (y) ^ (z))
+#define P(a,b,c,d,x,s)                      \
+    do                                      \
+    {                                       \
+        (a) += F(b,c,d) + (x) + 0x6ED9EBA1; \
+        (a) = S(a,s);                       \
+    } while( 0 )
 
     P( A, B, C, D, X[ 0],  3 );
     P( D, A, B, C, X[ 8],  9 );