diff --git a/thread.c b/thread.c
index d9d497ad6c..80550eeaaa 100644
--- a/thread.c
+++ b/thread.c
@@ -2471,7 +2471,7 @@ rb_fd_rcopy(fd_set *dst, rb_fdset_t *src)
 
     /* we assume src is the result of select() with dst, so dst should be
      * larger or equal than src. */
-    if (max > FD_SETSIZE || max > dst->fd_count) {
+    if (max > FD_SETSIZE || (UINT)max > dst->fd_count) {
 	rb_raise(rb_eArgError, "too large fdsets");
     }
 
diff --git a/win32/win32.c b/win32/win32.c
index 5851377ff2..fc1cd29b2d 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -3147,7 +3147,7 @@ overlapped_socket_io(BOOL input, int fd, char *buf, int len, int flags,
 {
     int r;
     int ret;
-    int mode;
+    int mode = 0;
     DWORD flg;
     WSAOVERLAPPED wol;
     WSABUF wbuf;
@@ -3282,7 +3282,7 @@ recvmsg(int fd, struct msghdr *msg, int flags)
     static WSARecvMsg_t pWSARecvMsg = NULL;
     WSAMSG wsamsg;
     SOCKET s;
-    int mode;
+    int mode = 0;
     DWORD len;
     int ret;
 
@@ -3340,7 +3340,7 @@ sendmsg(int fd, const struct msghdr *msg, int flags)
     static WSASendMsg_t pWSASendMsg = NULL;
     WSAMSG wsamsg;
     SOCKET s;
-    int mode;
+    int mode = 0;
     DWORD len;
     int ret;
 
@@ -3811,7 +3811,7 @@ dupfd(HANDLE hDup, char flags, int minfd)
 	    goto close_fds_and_return;
 	}
 	fds[filled++] = ret;
-    } while (filled < (sizeof(fds)/sizeof(fds[0])));
+    } while (filled < (int)numberof(fds));
 
     ret = dupfd(hDup, flags, minfd);