diff --git a/mongoose.c b/mongoose.c
index d24aaa6f..91283fe3 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -4216,7 +4216,7 @@ static void mkpay(struct pkt *pkt, void *p) {
 static uint32_t csumup(uint32_t sum, const void *buf, size_t len) {
   size_t i;
   const uint8_t *p = (const uint8_t *) buf;
-  for (i = 0; i < len; i++) sum += i & 1 ? p[i] : (uint32_t) (p[i] << 8);
+  for (i = 0; i < len; i++) sum += i & 1 ? p[i] : ((uint32_t) p[i]) << 8;
   return sum;
 }
 
diff --git a/src/net_builtin.c b/src/net_builtin.c
index 6576bde5..e37ab9a2 100644
--- a/src/net_builtin.c
+++ b/src/net_builtin.c
@@ -152,7 +152,7 @@ static void mkpay(struct pkt *pkt, void *p) {
 static uint32_t csumup(uint32_t sum, const void *buf, size_t len) {
   size_t i;
   const uint8_t *p = (const uint8_t *) buf;
-  for (i = 0; i < len; i++) sum += i & 1 ? p[i] : (uint32_t) (p[i] << 8);
+  for (i = 0; i < len; i++) sum += i & 1 ? p[i] : ((uint32_t) p[i]) << 8;
   return sum;
 }