diff --git a/src/afd.c b/src/afd.c
index a3ff7bf..27df0e7 100644
--- a/src/afd.c
+++ b/src/afd.c
@@ -8,7 +8,6 @@
 #include "win.h"
 #include "ws.h"
 
-#define _AFD_ANY_PROTOCOL -1
 #define IOCTL_AFD_POLL 0x00012024
 
 /* clang-format off */
@@ -27,6 +26,8 @@ static const GUID _AFD_PROVIDER_GUID_LIST[] = {
    {0xb6, 0x55, 0x00, 0x80, 0x5f, 0x36, 0x42, 0xcc}}};
 /* clang-format on */
 
+static const int _AFD_ANY_PROTOCOL = -1;
+
 /* This protocol info record is used by afd_create_driver_socket() to create
  * sockets that can be used as the first argument to afd_poll(). It is
  * populated on startup by afd_global_init(). */
diff --git a/src/error.c b/src/error.c
index 958061f..ac208b8 100644
--- a/src/error.c
+++ b/src/error.c
@@ -3,7 +3,7 @@
 #include "error.h"
 #include "win.h"
 
-#define _ERROR_ERRNO_MAP(X)                  \
+#define ERR__ERRNO_MAPPINGS(X)               \
   X(ERROR_ACCESS_DENIED, EACCES)             \
   X(ERROR_ALREADY_EXISTS, EEXIST)            \
   X(ERROR_BAD_COMMAND, EACCES)               \
@@ -111,7 +111,7 @@ static errno_t _err_map_win_error_to_errno(DWORD error) {
 #define X(error_sym, errno_sym) \
   case error_sym:               \
     return errno_sym;
-    _ERROR_ERRNO_MAP(X)
+    ERR__ERRNO_MAPPINGS(X)
 #undef X
   }
   return EINVAL;
diff --git a/src/port.c b/src/port.c
index 53b3fa5..0f51033 100644
--- a/src/port.c
+++ b/src/port.c
@@ -14,7 +14,7 @@
 #include "wepoll.h"
 #include "win.h"
 
-#define _PORT_MAX_ON_STACK_COMPLETIONS 256
+#define EP_PORT__MAX_ON_STACK_COMPLETIONS 256
 
 static ep_port_t* _ep_port_alloc(void) {
   ep_port_t* port_info = malloc(sizeof *port_info);
@@ -195,7 +195,7 @@ int ep_port_wait(ep_port_t* port_info,
                  struct epoll_event* events,
                  int maxevents,
                  int timeout) {
-  OVERLAPPED_ENTRY stack_iocp_events[_PORT_MAX_ON_STACK_COMPLETIONS];
+  OVERLAPPED_ENTRY stack_iocp_events[EP_PORT__MAX_ON_STACK_COMPLETIONS];
   OVERLAPPED_ENTRY* iocp_events;
   uint64_t due = 0;
   DWORD gqcs_timeout;
diff --git a/src/sock.c b/src/sock.c
index 0f35d64..a493b44 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -11,9 +11,9 @@
 #include "sock.h"
 #include "ws.h"
 
-#define _KNOWN_EPOLL_EVENTS                                            \
-  (EPOLLIN | EPOLLPRI | EPOLLOUT | EPOLLERR | EPOLLHUP | EPOLLRDNORM | \
-   EPOLLRDBAND | EPOLLWRNORM | EPOLLWRBAND | EPOLLRDHUP)
+static const uint32_t _EP_SOCK_KNOWN_EPOLL_EVENTS =
+    EPOLLIN | EPOLLPRI | EPOLLOUT | EPOLLERR | EPOLLHUP | EPOLLRDNORM |
+    EPOLLRDBAND | EPOLLWRNORM | EPOLLWRBAND | EPOLLMSG | EPOLLRDHUP;
 
 typedef enum _poll_status {
   _POLL_IDLE = 0,
@@ -151,7 +151,7 @@ int ep_sock_set_event(ep_port_t* port_info,
   sock_info->user_events = events;
   sock_info->user_data = ev->data;
 
-  if ((events & _KNOWN_EPOLL_EVENTS & ~sock_info->pending_events) != 0)
+  if ((events & _EP_SOCK_KNOWN_EPOLL_EVENTS & ~sock_info->pending_events) != 0)
     ep_port_request_socket_update(port_info, sock_info);
 
   return 0;
@@ -201,7 +201,7 @@ int ep_sock_update(ep_port_t* port_info, ep_sock_t* sock_info) {
   assert(!sock_info->delete_pending);
 
   if ((sock_info->poll_status == _POLL_PENDING) &&
-      (sock_info->user_events & _KNOWN_EPOLL_EVENTS &
+      (sock_info->user_events & _EP_SOCK_KNOWN_EPOLL_EVENTS &
        ~sock_info->pending_events) == 0) {
     /* All the events the user is interested in are already being monitored by
      * the pending poll operation. It might spuriously complete because of an
diff --git a/src/tree.c b/src/tree.c
index d69e391..537508e 100644
--- a/src/tree.c
+++ b/src/tree.c
@@ -13,7 +13,7 @@ void tree_node_init(tree_node_t* node) {
   memset(node, 0, sizeof *node);
 }
 
-#define _TREE_ROTATE(cis, trans)   \
+#define TREE__ROTATE(cis, trans)   \
   tree_node_t* p = node;           \
   tree_node_t* q = node->trans;    \
   tree_node_t* parent = p->parent; \
@@ -35,14 +35,14 @@ void tree_node_init(tree_node_t* node) {
   q->cis = p;
 
 static inline void _tree_rotate_left(tree_t* tree, tree_node_t* node) {
-  _TREE_ROTATE(left, right)
+  TREE__ROTATE(left, right)
 }
 
 static inline void _tree_rotate_right(tree_t* tree, tree_node_t* node) {
-  _TREE_ROTATE(right, left)
+  TREE__ROTATE(right, left)
 }
 
-#define _TREE_INSERT_OR_DESCEND(side) \
+#define TREE__INSERT_OR_DESCEND(side) \
   if (parent->side) {                 \
     parent = parent->side;            \
   } else {                            \
@@ -50,7 +50,7 @@ static inline void _tree_rotate_right(tree_t* tree, tree_node_t* node) {
     break;                            \
   }
 
-#define _TREE_FIXUP_AFTER_INSERT(cis, trans) \
+#define TREE__FIXUP_AFTER_INSERT(cis, trans) \
   tree_node_t* grandparent = parent->parent; \
   tree_node_t* uncle = grandparent->trans;   \
                                              \
@@ -76,9 +76,9 @@ int tree_add(tree_t* tree, tree_node_t* node, uintptr_t key) {
   if (parent) {
     for (;;) {
       if (key < parent->key) {
-        _TREE_INSERT_OR_DESCEND(left)
+        TREE__INSERT_OR_DESCEND(left)
       } else if (key > parent->key) {
-        _TREE_INSERT_OR_DESCEND(right)
+        TREE__INSERT_OR_DESCEND(right)
       } else {
         return -1;
       }
@@ -94,9 +94,9 @@ int tree_add(tree_t* tree, tree_node_t* node, uintptr_t key) {
 
   for (; parent && parent->red; parent = node->parent) {
     if (parent == parent->parent->left) {
-      _TREE_FIXUP_AFTER_INSERT(left, right)
+      TREE__FIXUP_AFTER_INSERT(left, right)
     } else {
-      _TREE_FIXUP_AFTER_INSERT(right, left)
+      TREE__FIXUP_AFTER_INSERT(right, left)
     }
   }
   tree->root->red = false;
@@ -104,7 +104,7 @@ int tree_add(tree_t* tree, tree_node_t* node, uintptr_t key) {
   return 0;
 }
 
-#define _TREE_FIXUP_AFTER_REMOVE(cis, trans)       \
+#define TREE__FIXUP_AFTER_REMOVE(cis, trans)       \
   tree_node_t* sibling = parent->trans;            \
                                                    \
   if (sibling->red) {                              \
@@ -190,9 +190,9 @@ void tree_del(tree_t* tree, tree_node_t* node) {
     if (node == tree->root)
       break;
     if (node == parent->left) {
-      _TREE_FIXUP_AFTER_REMOVE(left, right)
+      TREE__FIXUP_AFTER_REMOVE(left, right)
     } else {
-      _TREE_FIXUP_AFTER_REMOVE(right, left)
+      TREE__FIXUP_AFTER_REMOVE(right, left)
     }
     node = parent;
     parent = parent->parent;
diff --git a/src/ws.c b/src/ws.c
index 46be284..af88ec7 100644
--- a/src/ws.c
+++ b/src/ws.c
@@ -10,7 +10,7 @@
 #define SIO_BASE_HANDLE 0x48000022
 #endif
 
-#define _WS_INITIAL_CATALOG_BUFFER_SIZE 0x4000 /* 16kb. */
+#define WS__INITIAL_CATALOG_BUFFER_SIZE 0x4000 /* 16kb. */
 
 int ws_global_init(void) {
   int r;
@@ -45,7 +45,7 @@ SOCKET ws_get_base_socket(SOCKET socket) {
  * The infos pointer must be released by the caller with free(). */
 int ws_get_protocol_catalog(WSAPROTOCOL_INFOW** infos_out,
                             size_t* infos_count_out) {
-  DWORD buffer_size = _WS_INITIAL_CATALOG_BUFFER_SIZE;
+  DWORD buffer_size = WS__INITIAL_CATALOG_BUFFER_SIZE;
   int count;
   WSAPROTOCOL_INFOW* infos;
 
diff --git a/test/shared/test-util.h b/test/shared/test-util.h
index c9c9dd3..68c9497 100644
--- a/test/shared/test-util.h
+++ b/test/shared/test-util.h
@@ -21,16 +21,16 @@
 
 void no_inline no_return check_fail(const char* message);
 
-#define __check_to_string_helper(v) #v
-#define __check_to_string(v) __check_to_string_helper(v)
+#define _check_to_string_helper(v) #v
+#define _check_to_string(v) _check_to_string_helper(v)
 
-#define check(expression)                                           \
-  (void) ((!!(expression)) ||                                       \
-          (check_fail("\n"                                          \
-                      "Check failed:\n"                             \
-                      "  test: " #expression "\n"                   \
-                      "  file: " __FILE__ "\n"                      \
-                      "  line: " __check_to_string(__LINE__) "\n"), \
+#define check(expression)                                          \
+  (void) ((!!(expression)) ||                                      \
+          (check_fail("\n"                                         \
+                      "Check failed:\n"                            \
+                      "  test: " #expression "\n"                  \
+                      "  file: " __FILE__ "\n"                     \
+                      "  line: " _check_to_string(__LINE__) "\n"), \
            0))
 
 #endif /* TEST_UTIL_H_ */