diff --git a/library/md5.c b/library/md5.c
index 2a740cd..bdbb760 100644
--- a/library/md5.c
+++ b/library/md5.c
@@ -136,19 +136,22 @@
     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) ) ) )
 
-#define P(a,b,c,d,k,s,t)                                \
-{                                                       \
-    a += F(b,c,d) + X[k] + t; a = S(a,s) + b;           \
-}
+#define P(a,b,c,d,k,s,t)                                        \
+    do                                                          \
+    {                                                           \
+        (a) += F((b),(c),(d)) + X[k] + (t);                     \
+        (a) = S((a),(s)) + (b);                                 \
+    } while( 0 )
 
     A = ctx->state[0];
     B = ctx->state[1];
     C = ctx->state[2];
     D = ctx->state[3];
 
-#define F(x,y,z) (z ^ (x & (y ^ z)))
+#define F(x,y,z) ((z) ^ ((x) & ((y) ^ (z))))
 
     P( A, B, C, D,  0,  7, 0xD76AA478 );
     P( D, A, B, C,  1, 12, 0xE8C7B756 );
@@ -169,7 +172,7 @@
 
 #undef F
 
-#define F(x,y,z) (y ^ (z & (x ^ y)))
+#define F(x,y,z) ((y) ^ ((z) & ((x) ^ (y))))
 
     P( A, B, C, D,  1,  5, 0xF61E2562 );
     P( D, A, B, C,  6,  9, 0xC040B340 );
@@ -190,7 +193,7 @@
 
 #undef F
 
-#define F(x,y,z) (x ^ y ^ z)
+#define F(x,y,z) ((x) ^ (y) ^ (z))
 
     P( A, B, C, D,  5,  4, 0xFFFA3942 );
     P( D, A, B, C,  8, 11, 0x8771F681 );
@@ -211,7 +214,7 @@
 
 #undef F
 
-#define F(x,y,z) (y ^ (x | ~z))
+#define F(x,y,z) ((y) ^ ((x) | ~(z)))
 
     P( A, B, C, D,  0,  6, 0xF4292244 );
     P( D, A, B, C,  7, 10, 0x432AFF97 );