diff --git a/src/runtime/runtime-gdb_test.go b/src/runtime/runtime-gdb_test.go
index 2818ada..7cfd5b9 100644
--- a/src/runtime/runtime-gdb_test.go
+++ b/src/runtime/runtime-gdb_test.go
@@ -19,6 +19,12 @@
 	"testing"
 )
 
+// NOTE: In some configurations, GDB will segfault when sent a SIGWINCH signal.
+// Some runtime tests send SIGWINCH to the entire process group, so those tests
+// must never run in parallel with GDB tests.
+//
+// See issue 39021 and https://sourceware.org/bugzilla/show_bug.cgi?id=26056.
+
 func checkGdbEnvironment(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
 	switch runtime.GOOS {
diff --git a/src/runtime/testdata/testprogcgo/eintr.go b/src/runtime/testdata/testprogcgo/eintr.go
index 9d9435d..791ff1b 100644
--- a/src/runtime/testdata/testprogcgo/eintr.go
+++ b/src/runtime/testdata/testprogcgo/eintr.go
@@ -89,8 +89,9 @@
 func winch() {
 	ticker := time.NewTicker(100 * time.Microsecond)
 	defer ticker.Stop()
+	pid := syscall.Getpid()
 	for n := 10; n > 0; n-- {
-		syscall.Kill(0, syscall.SIGWINCH)
+		syscall.Kill(pid, syscall.SIGWINCH)
 		<-ticker.C
 	}
 }