diff --git a/src/flag/flag.go b/src/flag/flag.go
index 45928b01906f26..9d3e8d32a5a407 100644
--- a/src/flag/flag.go
+++ b/src/flag/flag.go
@@ -89,6 +89,7 @@ import (
 	"io"
 	"os"
 	"reflect"
+	"runtime"
 	"sort"
 	"strconv"
 	"strings"
@@ -399,7 +400,8 @@ type FlagSet struct {
 	formal        map[string]*Flag
 	args          []string // arguments after flags
 	errorHandling ErrorHandling
-	output        io.Writer // nil means stderr; use Output() accessor
+	output        io.Writer         // nil means stderr; use Output() accessor
+	undef         map[string]string // flags which didn't exist at the time of Set
 }
 
 // A Flag represents the state of a flag.
@@ -490,8 +492,29 @@ func Lookup(name string) *Flag {
 
 // Set sets the value of the named flag.
 func (f *FlagSet) Set(name, value string) error {
+	return f.set(name, value)
+}
+func (f *FlagSet) set(name, value string) error {
 	flag, ok := f.formal[name]
 	if !ok {
+		// Remember that a flag that isn't defined is being set.
+		// We return an error in this case, but in addition if
+		// subsequently that flag is defined, we want to panic
+		// at the definition point.
+		// This is a problem which occurs if both the definition
+		// and the Set call are in init code and for whatever
+		// reason the init code changes evaluation order.
+		// See issue 57411.
+		_, file, line, ok := runtime.Caller(2)
+		if !ok {
+			file = "?"
+			line = 0
+		}
+		if f.undef == nil {
+			f.undef = map[string]string{}
+		}
+		f.undef[name] = fmt.Sprintf("%s:%d", file, line)
+
 		return fmt.Errorf("no such flag -%v", name)
 	}
 	err := flag.Value.Set(value)
@@ -507,7 +530,7 @@ func (f *FlagSet) Set(name, value string) error {
 
 // Set sets the value of the named command-line flag.
 func Set(name, value string) error {
-	return CommandLine.Set(name, value)
+	return CommandLine.set(name, value)
 }
 
 // isZeroValue determines whether the string represents the zero
@@ -1004,6 +1027,9 @@ func (f *FlagSet) Var(value Value, name string, usage string) {
 		}
 		panic(msg) // Happens only if flags are declared with identical names
 	}
+	if pos := f.undef[name]; pos != "" {
+		panic(fmt.Sprintf("flag %s set at %s before being defined", name, pos))
+	}
 	if f.formal == nil {
 		f.formal = make(map[string]*Flag)
 	}
diff --git a/src/flag/flag_test.go b/src/flag/flag_test.go
index 14d199d6e950a8..57c88f009f1c4f 100644
--- a/src/flag/flag_test.go
+++ b/src/flag/flag_test.go
@@ -12,6 +12,7 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"regexp"
 	"runtime"
 	"sort"
 	"strconv"
@@ -726,7 +727,7 @@ func mustPanic(t *testing.T, testName string, expected string, f func()) {
 		case nil:
 			t.Errorf("%s\n: expected panic(%q), but did not panic", testName, expected)
 		case string:
-			if msg != expected {
+			if ok, _ := regexp.MatchString(expected, msg); !ok {
 				t.Errorf("%s\n: expected panic(%q), but got panic(%q)", testName, expected, msg)
 			}
 		default:
@@ -844,3 +845,14 @@ func TestUserDefinedBoolFunc(t *testing.T) {
 		t.Errorf(`got %q; error should contain "test error"`, errMsg)
 	}
 }
+
+func TestDefineAfterSet(t *testing.T) {
+	flags := NewFlagSet("test", ContinueOnError)
+	// Set by itself doesn't panic.
+	flags.Set("myFlag", "value")
+
+	// Define-after-set panics.
+	mustPanic(t, "DefineAfterSet", "flag myFlag set at .*/flag_test.go:.* before being defined", func() {
+		_ = flags.String("myFlag", "default", "usage")
+	})
+}