diff --git a/src/cmd/link/doc.go b/src/cmd/link/doc.go
index d61b66a938..963d86a35f 100644
--- a/src/cmd/link/doc.go
+++ b/src/cmd/link/doc.go
@@ -39,8 +39,10 @@ Flags:
 		Print linker version and exit.
 	-X importpath.name=value
 		Set the value of the string variable in importpath named name to value.
+		This is only effective if the variable is declared in the source code either uninitialized
+		or initialized to a constant string expression. -X will not work if the initializer makes
+		a function call or refers to other variables.
 		Note that before Go 1.5 this option took two separate arguments.
-		Now it takes one argument split on the first = sign.
 	-buildmode mode
 		Set build mode (default exe).
 	-cpuprofile file
diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index 93c77c006b..c337c5e7ed 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -828,6 +828,7 @@ func addstrdata1(ctxt *Link, arg string) {
 	strdata[name] = value
 }
 
+// addstrdata sets the initial value of the string variable name to value.
 func addstrdata(ctxt *Link, name, value string) {
 	s := ctxt.Syms.ROLookup(name, 0)
 	if s == nil || s.Gotype == nil {