added (char *) casts
diff --git a/progs/demos/terrain.c b/progs/demos/terrain.c
index da5b90d..9063c93 100644
--- a/progs/demos/terrain.c
+++ b/progs/demos/terrain.c
@@ -572,7 +572,7 @@
    if ((gluerr = gluBuild2DMipmaps(GL_TEXTURE_2D, 1, 256, 256, GL_LUMINANCE,
 				   GL_UNSIGNED_BYTE,
 				   (GLvoid *) (&terrainpic[0])))) {
-      fprintf(stderr, "GLULib%s\n", gluErrorString(gluerr));
+      fprintf(stderr, "GLULib%s\n", (char *) gluErrorString(gluerr));
       exit(-1);
    }