--- overlay_gl/overlay_gl.pro	2017-01-29 23:44:01.966483578 +0100
+++ overlay_gl/overlay_gl.pro	2017-01-29 23:44:24.487186063 +0100
@@ -7,7 +7,7 @@
 TARGET = mumble$(TARGET_ADD)
 VERSION = 1.2.19
 SOURCES = overlay.c
-LIBS *= -lrt -ldl
+LIBS *= -lGL -lrt -ldl
 QMAKE_CFLAGS *= -fvisibility=hidden $(CFLAGS_ADD)
 QMAKE_LFLAGS -= -Wl,--no-undefined
 QMAKE_LFLAGS *= $(LFLAGS_ADD)