diff --git a/src/api/netdb.c b/src/api/netdb.c
index d1f134ce..3185cfb6 100644
--- a/src/api/netdb.c
+++ b/src/api/netdb.c
@@ -326,7 +326,8 @@ lwip_getaddrinfo(const char *nodename, const char *servname,
   if (nodename != NULL) {
     /* copy nodename to canonname if specified */
     size_t namelen = strlen(nodename);
-    ai->ai_canonname = mem_malloc(namelen + 1);
+    LWIP_ASSERT("namelen is too long", (namelen + 1) <= (mem_size_t)-1);
+    ai->ai_canonname = mem_malloc((mem_size_t)(namelen + 1));
     if (ai->ai_canonname == NULL) {
       goto memerr;
     }
diff --git a/src/core/sys.c b/src/core/sys.c
index c5a643b9..d1fbda4e 100644
--- a/src/core/sys.c
+++ b/src/core/sys.c
@@ -65,7 +65,7 @@ struct sswt_cb
 void
 sys_mbox_fetch(sys_mbox_t mbox, void **msg)
 {
-  u32_t time;
+  u32_t time_needed;
   struct sys_timeouts *timeouts;
   struct sys_timeo *tmptimeout;
   sys_timeout_handler h;
@@ -76,18 +76,18 @@ sys_mbox_fetch(sys_mbox_t mbox, void **msg)
 
   if (!timeouts || !timeouts->next) {
     UNLOCK_TCPIP_CORE();
-    time = sys_arch_mbox_fetch(mbox, msg, 0);
+    time_needed = sys_arch_mbox_fetch(mbox, msg, 0);
     LOCK_TCPIP_CORE();
   } else {
     if (timeouts->next->time > 0) {
       UNLOCK_TCPIP_CORE();
-      time = sys_arch_mbox_fetch(mbox, msg, timeouts->next->time);
+      time_needed = sys_arch_mbox_fetch(mbox, msg, timeouts->next->time);
       LOCK_TCPIP_CORE();
     } else {
-      time = SYS_ARCH_TIMEOUT;
+      time_needed = SYS_ARCH_TIMEOUT;
     }
 
-    if (time == SYS_ARCH_TIMEOUT) {
+    if (time_needed == SYS_ARCH_TIMEOUT) {
       /* If time == SYS_ARCH_TIMEOUT, a timeout occured before a message
          could be fetched. We should now call the timeout handler and
          deallocate the memory allocated for the timeout. */
@@ -107,8 +107,8 @@ sys_mbox_fetch(sys_mbox_t mbox, void **msg)
       /* If time != SYS_ARCH_TIMEOUT, a message was received before the timeout
          occured. The time variable is set to the number of
          milliseconds we waited for the message. */
-      if (time < timeouts->next->time) {
-        timeouts->next->time -= time;
+      if (time_needed < timeouts->next->time) {
+        timeouts->next->time -= time_needed;
       } else {
         timeouts->next->time = 0;
       }
@@ -125,7 +125,7 @@ sys_mbox_fetch(sys_mbox_t mbox, void **msg)
 void
 sys_sem_wait(sys_sem_t sem)
 {
-  u32_t time;
+  u32_t time_needed;
   struct sys_timeouts *timeouts;
   struct sys_timeo *tmptimeout;
   sys_timeout_handler h;
@@ -139,12 +139,12 @@ sys_sem_wait(sys_sem_t sem)
     sys_arch_sem_wait(sem, 0);
   } else {
     if (timeouts->next->time > 0) {
-      time = sys_arch_sem_wait(sem, timeouts->next->time);
+      time_needed = sys_arch_sem_wait(sem, timeouts->next->time);
     } else {
-      time = SYS_ARCH_TIMEOUT;
+      time_needed = SYS_ARCH_TIMEOUT;
     }
 
-    if (time == SYS_ARCH_TIMEOUT) {
+    if (time_needed == SYS_ARCH_TIMEOUT) {
       /* If time == SYS_ARCH_TIMEOUT, a timeout occured before a message
         could be fetched. We should now call the timeout handler and
         deallocate the memory allocated for the timeout. */
@@ -164,8 +164,8 @@ sys_sem_wait(sys_sem_t sem)
       /* If time != SYS_ARCH_TIMEOUT, a message was received before the timeout
          occured. The time variable is set to the number of
          milliseconds we waited for the message. */
-      if (time < timeouts->next->time) {
-        timeouts->next->time -= time;
+      if (time_needed < timeouts->next->time) {
+        timeouts->next->time -= time_needed;
       } else {
         timeouts->next->time = 0;
       }
diff --git a/src/include/lwip/debug.h b/src/include/lwip/debug.h
index 089a80aa..d5c4e474 100644
--- a/src/include/lwip/debug.h
+++ b/src/include/lwip/debug.h
@@ -61,26 +61,28 @@
 #define LWIP_DBG_HALT          0x08U
 
 #ifndef LWIP_NOASSERT
-#define LWIP_ASSERT(x,y) do { if(!(y)) LWIP_PLATFORM_ASSERT(x); } while(0)
+#define LWIP_ASSERT(message, assertion) do { if(!(assertion)) \
+  LWIP_PLATFORM_ASSERT(message); } while(0)
 #else  /* LWIP_NOASSERT */
-#define LWIP_ASSERT(x,y) 
+#define LWIP_ASSERT(message, assertion) 
 #endif /* LWIP_NOASSERT */
 
-/** if "e" isn't true, then print "m" message and execute "h" expression */
+/** if "expression" isn't true, then print "message" and execute "handler" expression */
 #ifndef LWIP_ERROR
-#define LWIP_ERROR(m,e,h) do { if (!(e)) { LWIP_PLATFORM_ASSERT(m); h;}} while(0)
+#define LWIP_ERROR(message, expression, handler) do { if (!(expression)) { \
+  LWIP_PLATFORM_ASSERT(message); handler;}} while(0)
 #endif /* LWIP_ERROR */
 
 #ifdef LWIP_DEBUG
 /** print debug message only if debug message type is enabled...
  *  AND is of correct type AND is at least LWIP_DBG_LEVEL
  */
-#define LWIP_DEBUGF(debug,x) do { \
+#define LWIP_DEBUGF(debug, message) do { \
                                if ( \
                                    ((debug) & LWIP_DBG_ON) && \
                                    ((debug) & LWIP_DBG_TYPES_ON) && \
                                    ((s16_t)((debug) & LWIP_DBG_MASK_LEVEL) >= LWIP_DBG_MIN_LEVEL)) { \
-                                 LWIP_PLATFORM_DIAG(x); \
+                                 LWIP_PLATFORM_DIAG(message); \
                                  if ((debug) & LWIP_DBG_HALT) { \
                                    while(1); \
                                  } \
@@ -88,7 +90,7 @@
                              } while(0)
 
 #else  /* LWIP_DEBUG */
-#define LWIP_DEBUGF(debug,x) 
+#define LWIP_DEBUGF(debug, message) 
 #endif /* LWIP_DEBUG */
 
 #endif /* __LWIP_DEBUG_H__ */