diff --git a/src/partiviewc.cc b/src/partiviewc.cc
index 93c6f87fbfee4b0d524f13c23ac64bff682f9b5b..16cd9737dfdd44089f66bed6f712cabfd1ab99b5 100644
--- a/src/partiviewc.cc
+++ b/src/partiviewc.cc
@@ -20,6 +20,14 @@
 
 #include <FL/glut.H>	/* for GLUT_STEREO if FLTK knows it */
 
+#ifndef GLUT_STEREO
+# if unix
+#  include <FL/x.H>	/* otherwise, need GLX symbols for X-specific stereo */
+#  include <GL/glx.h>
+# endif
+#endif
+
+
 #include <ctype.h>
 #undef isspace		/* hack for irix 6.5 */