diff --git a/src/runtime/pprof/pprof.go b/src/runtime/pprof/pprof.go
index d32b31578d..7d677cb64e 100644
--- a/src/runtime/pprof/pprof.go
+++ b/src/runtime/pprof/pprof.go
@@ -567,6 +567,14 @@ var cpu struct {
 // StartCPUProfile enables CPU profiling for the current process.
 // While profiling, the profile will be buffered and written to w.
 // StartCPUProfile returns an error if profiling is already enabled.
+//
+// On Unix-like systems, StartCPUProfile does not work by default for
+// Go code built with -buildmode=c-archive or -buildmode=c-shared.
+// StartCPUProfile relies on the SIGPROF signal, but that signal will
+// be delivered to the main program's SIGPROF signal handler (if any)
+// not to the one used by Go.  To make it work, call os/signal.Notify
+// for syscall.SIGPROF, but note that doing so may break any profiling
+// being done by the main program.
 func StartCPUProfile(w io.Writer) error {
 	// The runtime routines allow a variable profiling rate,
 	// but in practice operating systems cannot trigger signals