OpenBSD also needs the _XOPEN_SOURCE_EXTENDED define.

Index: ttyplot.c
--- ttyplot.c.orig
+++ ttyplot.c
@@ -8,7 +8,7 @@
 
 // This is needed on FreeBSD and macOS to get the ncurses widechar API,
 // and pkg-config fails to define it.
-#if defined(__APPLE__) || defined(__FreeBSD__)
+#if defined(__APPLE__) || defined(__FreeBSD__) || defined(__OpenBSD__)
 #define _XOPEN_SOURCE_EXTENDED
 #else
 // This is needed for musl libc
@@ -923,10 +923,6 @@ int main(int argc, char *argv[]) {
         exit(1);
     }
 
-#ifdef __OpenBSD__
-    if (pledge("stdio tty", NULL) == -1)
-        err(1, "pledge");
-#endif
 
     // Check if any colors are defined
     bool has_colors = false;
@@ -986,6 +982,11 @@ int main(int argc, char *argv[]) {
 
     signal(SIGWINCH, signal_handler);
     signal(SIGINT, signal_handler);
+
+#ifdef __OpenBSD__
+    if (pledge("stdio tty", NULL) == -1)
+        err(1, "pledge");
+#endif
 
     while (1) {
         struct timeval timeout = calculate_clock_refresh_timeout_from(now.tv_usec);