--- origsrc/geomview-1.9.5/src/lib/mg/opengl/mgopenglshade.c	2014-03-12 12:51:13.000000000 -0400
+++ src/geomview-1.9.5/src/lib/mg/opengl/mgopenglshade.c	2017-06-09 10:25:41.647550600 -0400
@@ -413,10 +413,15 @@ mgopengl_lightmodeldef(int lightmodel, L
  *	  supports it;
  *  - or, if we're on a system that claims to support it at compile time,
  *	  we'll just hope that that system also supports it at run time.
+ * But Cygwin does not support weak symbols, and the use of "#pragma
+ * weak" causes "undefined symbol" errors when linking on x86_64
+ * Cygwin.
  */
 
+#ifndef __CYGWIN__
 # pragma weak glBindTextureEXT
 # pragma weak glDeleteTexturesEXT
+#endif
 
 # ifndef GL_EXT_texture_object
 /* If <GL/gl.h> doesn't know about glBindTextureEXT etc., declare here. */