diff --git a/fail_db.txt b/fail_db.txt
index 59e0a7a6..eb3c0fe9 100644
--- a/fail_db.txt
+++ b/fail_db.txt
@@ -1,4 +1,11 @@
-% List of known fails
+% List of known fails.
+% The list is unordered and contains information about commonly used platforms / configurations.
+% Our goas is to maintain this list for Linux, MacOS and Windows with reasonably new compilers.
+% Note, that it's important which C++ compiler was used. For example, gcc 4.4 is know to produce
+% considerably more fails with generic targets, than gcc 4.7 or later.
+% Using old compilers (gcc 4.4 is considered to be relatively old) may cause LLVM bugs.
+% To avoid them you can use LLVM selfbuild.
+% 
 ./tests/masked-scatter-vector.ispc runfail  x86-64     sse2-i32x4   Linux LLVM 3.3     g++4.4 -O2 *
 ./tests/atomics-13.ispc compfail     x86     sse4-i16x8   Linux LLVM 3.3     g++4.4 -O2 *
 ./tests/reduce-equal-10.ispc compfail     x86     sse4-i16x8   Linux LLVM 3.3     g++4.4 -O2 *