diff --git a/clang/test/CodeGen/enum.c b/clang/test/CodeGen/enum.c
index 87b0e1e..0e239f1 100644
--- a/clang/test/CodeGen/enum.c
+++ b/clang/test/CodeGen/enum.c
@@ -1,6 +1,9 @@
 // RUN: %clang_cc1 -triple i386-unknown-unknown %s -O3 -emit-llvm -o - | grep 'ret i32 6'
 // RUN: %clang_cc1 -triple i386-unknown-unknown -x c++ %s -O3 -emit-llvm -o - | grep 'ret i32 7'
 
+// This test case illustrates a peculiarity of the promotion of
+// enumeration types in C and C++. In particular, the enumeration type
+// "z" below promotes to an unsigned int in C but int in C++.
 static enum { foo, bar = 1U } z;
 
 int main (void)