diff --git a/panda/src/glxdisplay/glxGraphicsStateGuardian.h b/panda/src/glxdisplay/glxGraphicsStateGuardian.h
index db7e6ea3bf..5ad3e39400 100644
--- a/panda/src/glxdisplay/glxGraphicsStateGuardian.h
+++ b/panda/src/glxdisplay/glxGraphicsStateGuardian.h
@@ -47,6 +47,7 @@
 // these functions are defined, and the system glx.h sometimes doesn't
 // declare these typedefs.
 typedef __GLXextFuncPtr (* PFNGLXGETPROCADDRESSPROC) (const GLubyte *procName);
+typedef int (* PFNGLXSWAPINTERVALSGIPROC) (int interval);
 
 ////////////////////////////////////////////////////////////////////
 //       Class : glxGraphicsStateGuardian