diff --git a/files/root-5.20.00-include-defines-file.patch b/files/root-5.20.00-include-defines-file.patch
new file mode 100644
index 0000000..6c68e56
--- /dev/null
+++ b/files/root-5.20.00-include-defines-file.patch
@@ -0,0 +1,9 @@
+diff --git a/graf3d/gl/src/TGLFontManager.cxx b/graf3d/gl/src/TGLFontManager.cxx
+index 7863d64..2d6f405 100644
+--- a/graf3d/gl/src/TGLFontManager.cxx
++++ b/graf3d/gl/src/TGLFontManager.cxx
+@@ -1,3 +1,4 @@
++#include "RConfigure.h"
+ #include "TGLFontManager.h"
+ 
+ #include "TSystem.h"
diff --git a/root-5.20.00.ebuild b/root-5.20.00.ebuild
index 35b8a1c..68dfe57 100644
--- a/root-5.20.00.ebuild
+++ b/root-5.20.00.ebuild
@@ -88,6 +88,8 @@ src_unpack() {
 	cd "${S}"
 	epatch "${FILESDIR}"/${P}-configure.patch
 	epatch "${FILESDIR}"/${P}-pic.patch
+	# root bug; reported at https://savannah.cern.ch/bugs/?40816, fixed in svn
+	epatch "${FILESDIR}"/${PF}-include-defines-file.patch
 	# use system cfortran
 	if use cern; then
 		rm -f include/root/cfortran.h
-- 
1.6.0