diff --git a/GcToolchainTricks.md b/GcToolchainTricks.md
index 50797a54..1919754e 100644
--- a/GcToolchainTricks.md
+++ b/GcToolchainTricks.md
@@ -106,4 +106,4 @@ var BuildTime string
 
 You can build the program using this package using `go build -ldflags="-X 'company/buildinfo.BuildTime=$(date)'"` to record the build time in the string.  (The use of `$(date)` assumes you are using a Unix-style shell.)
 
-The string variable must exist, and it must be a variable, not a constant.  There is no warning for using the wrong name in the `-X` option.  You can often find the name to use by running `go tool nm` on the program, but that will fail if the package name has any non-ASCII characters, or a `"` or `%` character.
\ No newline at end of file
+The string variable must exist, it must be a variable, not a constant, and its value must not be initialized by a function call.  There is no warning for using the wrong name in the `-X` option.  You can often find the name to use by running `go tool nm` on the program, but that will fail if the package name has any non-ASCII characters, or a `"` or `%` character.
\ No newline at end of file