diff --git a/.github/workflows/gin.yml b/.github/workflows/gin.yml
index 4e3b8753..8ece7f1d 100644
--- a/.github/workflows/gin.yml
+++ b/.github/workflows/gin.yml
@@ -65,7 +65,7 @@ jobs:
         with:
           ref: ${{ github.ref }}
 
-      - uses: actions/cache@v4
+      - uses: actions/cache@v5
         with:
           path: |
             ${{ matrix.go-build }}
diff --git a/context_test.go b/context_test.go
index 61d435a6..f81abdae 100644
--- a/context_test.go
+++ b/context_test.go
@@ -1966,7 +1966,7 @@ func TestContextClientIP(t *testing.T) {
 	resetContextForClientIPTests(c)
 
 	// IPv6 support
-	c.Request.RemoteAddr = "[::1]:12345"
+	c.Request.RemoteAddr = fmt.Sprintf("[%s]:12345", localhostIPv6)
 	assert.Equal(t, "20.20.20.20", c.ClientIP())
 
 	resetContextForClientIPTests(c)
@@ -3268,7 +3268,7 @@ func TestContextCopyShouldNotCancel(t *testing.T) {
 	}()
 
 	addr := strings.Split(l.Addr().String(), ":")
-	res, err := http.Get(fmt.Sprintf("http://127.0.0.1:%s/", addr[len(addr)-1]))
+	res, err := http.Get(fmt.Sprintf("http://%s:%s/", localhostIP, addr[len(addr)-1]))
 	if err != nil {
 		t.Error(fmt.Errorf("request error: %w", err))
 		return
diff --git a/gin_test.go b/gin_test.go
index 81343d88..43c9494d 100644
--- a/gin_test.go
+++ b/gin_test.go
@@ -83,7 +83,7 @@ func TestLoadHTMLGlobDebugMode(t *testing.T) {
 }
 
 func TestH2c(t *testing.T) {
-	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	ln, err := net.Listen("tcp", localhostIP+":0")
 	if err != nil {
 		t.Error(err)
 	}
diff --git a/response_writer.go b/response_writer.go
index 6907e514..9035e6f1 100644
--- a/response_writer.go
+++ b/response_writer.go
@@ -128,7 +128,9 @@ func (w *responseWriter) CloseNotify() <-chan bool {
 // Flush implements the http.Flusher interface.
 func (w *responseWriter) Flush() {
 	w.WriteHeaderNow()
-	w.ResponseWriter.(http.Flusher).Flush()
+	if f, ok := w.ResponseWriter.(http.Flusher); ok {
+		f.Flush()
+	}
 }
 
 func (w *responseWriter) Pusher() (pusher http.Pusher) {
diff --git a/utils.go b/utils.go
index 971e9433..62517784 100644
--- a/utils.go
+++ b/utils.go
@@ -19,6 +19,12 @@ import (
 // BindKey indicates a default bind key.
 const BindKey = "_gin-gonic/gin/bindkey"
 
+// localhostIP indicates the default localhost IP address.
+const localhostIP = "127.0.0.1"
+
+// localhostIPv6 indicates the default localhost IPv6 address.
+const localhostIPv6 = "::1"
+
 // Bind is a helper function for given interface object and returns a Gin middleware.
 func Bind(val any) HandlerFunc {
 	value := reflect.ValueOf(val)