diff --git a/src/factor.c b/src/factor.c
index 2649e9fc6..802c05e4f 100644
--- a/src/factor.c
+++ b/src/factor.c
@@ -318,16 +318,16 @@ static void factor (uintmax_t, uintmax_t, struct factors *);
 #endif
 
 #define rsh2(rh, rl, ah, al, cnt)                                       \
-  do {                                                                  \
+  if (cnt) {                                                            \
     (rl) = ((ah) << (W_TYPE_SIZE - (cnt))) | ((al) >> (cnt));           \
     (rh) = (ah) >> (cnt);                                               \
-  } while (0)
+  } else (void) 0
 
 #define lsh2(rh, rl, ah, al, cnt)                                       \
-  do {                                                                  \
+  if (cnt) {                                                            \
     (rh) = ((ah) << cnt) | ((al) >> (W_TYPE_SIZE - (cnt)));             \
     (rl) = (al) << (cnt);                                               \
-  } while (0)
+  } else (void) 0
 
 #define ge2(ah, al, bh, bl)                                             \
   ((ah) > (bh) || ((ah) == (bh) && (al) >= (bl)))