diff -up megaglest-3.13.0/source/shared_lib/CMakeLists.txt.orig megaglest-3.13.0/source/shared_lib/CMakeLists.txt
--- megaglest-3.13.0/source/shared_lib/CMakeLists.txt.orig	2019-09-24 15:38:49.867482131 -0300
+++ megaglest-3.13.0/source/shared_lib/CMakeLists.txt	2019-09-24 15:39:00.045556832 -0300
@@ -109,7 +109,7 @@ IF(BUILD_MEGAGLEST_MODEL_VIEWER OR BUILD
 	FIND_PACKAGE(OpenGL REQUIRED)
 	INCLUDE_DIRECTORIES(${OPENGL_INCLUDE_DIR})
 	IF(UNIX)
-		SET(EXTERNAL_LIBS ${EXTERNAL_LIBS} ${OPENGL_LIBRARY})
+		SET(EXTERNAL_LIBS ${EXTERNAL_LIBS} ${OPENGL_LIBRARY} -lX11)
 	ENDIF()
 
 	FIND_PACKAGE(X11 REQUIRED)