diff --git a/ChangeLog b/ChangeLog
index f8be4dd0dc..5af0503160 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2012-10-18  Markus Trippelsdorf  <markus@trippelsdorf.de>
+
+	* math/Makefile: Comment on slow compilation of test-tgmath2.c.
+
 2012-10-18  Joseph Myers  <joseph@codesourcery.com>
 
 	* sysdeps/generic/_G_config.h (_G_OPEN64): Remove.
diff --git a/math/Makefile b/math/Makefile
index 7759873e63..9e17695dd3 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -126,6 +126,9 @@ CFLAGS-test-float.c = -fno-inline -ffloat-store -fno-builtin -frounding-math
 CFLAGS-test-double.c = -fno-inline -ffloat-store -fno-builtin -frounding-math
 CFLAGS-test-ldouble.c = -fno-inline -ffloat-store -fno-builtin -frounding-math
 CFLAGS-test-tgmath.c = -fno-builtin
+# The following testcase uses very long lines (>3 million), so it may take a
+# while to compile it. See: http://llvm.org/bugs/show_bug.cgi?id=14106 and
+# http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54402
 CFLAGS-test-tgmath2.c = -fno-builtin
 CFLAGS-test-tgmath-ret.c = -fno-builtin
 CFLAGS-test-powl.c = -fno-builtin