diff --git a/src/canvas/x11/x11.cpp b/src/canvas/x11/x11.cpp
index a308f70..f7b7f02 100644
--- a/src/canvas/x11/x11.cpp
+++ b/src/canvas/x11/x11.cpp
@@ -218,6 +218,7 @@ void X11Canvas::get_tmux_window_ids(std::unordered_set<xcb_window_t> &windows)
                 continue;
             }
             windows.insert(win->second);
+            break; // prevent multiple windows being created
         }
     }
 }
diff --git a/src/os.cpp b/src/os.cpp
index 8aefc3a..677a5dd 100644
--- a/src/os.cpp
+++ b/src/os.cpp
@@ -33,7 +33,7 @@ auto os::exec(const std::string &cmd) -> std::string
     const int bufsize = 128;
     std::array<char, bufsize> buffer;
     std::string result;
-    c_unique_ptr<FILE, pclose> pipe{popen(cmd.c_str(), "r")};
+    const c_unique_ptr<FILE, pclose> pipe{popen(cmd.c_str(), "r")};
     if (!pipe) {
         throw std::system_error(errno, std::generic_category());
     }
@@ -84,7 +84,7 @@ auto os::wait_for_data_on_fd(int filde, int waitms) -> bool
     poll(&fds, 1, waitms);
 
     if ((fds.revents & (POLLERR | POLLNVAL | POLLHUP)) != 0) {
-        throw std::system_error(errno, std::generic_category());
+        throw std::system_error(EIO, std::generic_category());
     }
 
     return (fds.revents & POLLIN) != 0;
@@ -116,14 +116,14 @@ auto os::get_ppid() -> int
 
 void os::daemonize()
 {
-    int pid = fork();
+    const int pid = fork();
     if (pid < 0) {
         std::exit(EXIT_FAILURE); // NOLINT
     }
     if (pid > 0) {
         std::exit(EXIT_SUCCESS); // NOLINT
     }
-    int status = setsid();
+    const int status = setsid();
     if (status < 0) {
         std::exit(EXIT_FAILURE); // NOLINT
     }
diff --git a/src/terminal.cpp b/src/terminal.cpp
index d564918..84c52fe 100644
--- a/src/terminal.cpp
+++ b/src/terminal.cpp
@@ -101,8 +101,8 @@ void Terminal::get_terminal_size()
 
     padding_horizontal = static_cast<uint16_t>(std::max(padding_horiz, padding_vert));
     padding_vertical = padding_horizontal;
-    font_width = std::ceil(guess_font_size(cols, xpixel, padding_horizontal));
-    font_height = std::ceil(guess_font_size(rows, ypixel, padding_vertical));
+    font_width = std::floor(guess_font_size(cols, xpixel, padding_horizontal));
+    font_height = std::floor(guess_font_size(rows, ypixel, padding_vertical));
 
     if (xpixel < fallback_xpixel && ypixel < fallback_ypixel) {
         padding_horizontal = (fallback_xpixel - xpixel) / 2;