diff --git a/gfx/display_servers/dispserv_x11.c b/gfx/display_servers/dispserv_x11.c
index e80fc89fdc..85741ddd1a 100644
--- a/gfx/display_servers/dispserv_x11.c
+++ b/gfx/display_servers/dispserv_x11.c
@@ -16,6 +16,7 @@
  */
 
 /* We are targeting XRandR 1.2 here. */
+#include <math.h>
 
 #include <compat/strl.h>