diff --git a/src/log/slog/handler.go b/src/log/slog/handler.go
index 47c7fd2782..cab0b5f088 100644
--- a/src/log/slog/handler.go
+++ b/src/log/slog/handler.go
@@ -110,7 +110,7 @@ func (h *defaultHandler) Handle(ctx context.Context, r Record) error {
 	buf.WriteString(r.Level.String())
 	buf.WriteByte(' ')
 	buf.WriteString(r.Message)
-	state := h.ch.newHandleState(buf, true, " ", nil)
+	state := h.ch.newHandleState(buf, true, " ")
 	defer state.free()
 	state.appendNonBuiltIns(r)
 	return h.output(r.PC, *buf)
@@ -186,11 +186,15 @@ type commonHandler struct {
 	json              bool // true => output JSON; false => output text
 	opts              HandlerOptions
 	preformattedAttrs []byte
-	groupPrefix       string   // for text: prefix of groups opened in preformatting
-	groups            []string // all groups started from WithGroup
-	nOpenGroups       int      // the number of groups opened in preformattedAttrs
-	mu                sync.Mutex
-	w                 io.Writer
+	// groupPrefix is for the text handler only.
+	// It holds the prefix for groups that were already pre-formatted.
+	// A group will appear here when a call to WithGroup is followed by
+	// a call to WithAttrs.
+	groupPrefix string
+	groups      []string // all groups started from WithGroup
+	nOpenGroups int      // the number of groups opened in preformattedAttrs
+	mu          sync.Mutex
+	w           io.Writer
 }
 
 func (h *commonHandler) clone() *commonHandler {
@@ -219,11 +223,9 @@ func (h *commonHandler) enabled(l Level) bool {
 func (h *commonHandler) withAttrs(as []Attr) *commonHandler {
 	h2 := h.clone()
 	// Pre-format the attributes as an optimization.
-	prefix := buffer.New()
-	defer prefix.Free()
-	prefix.WriteString(h.groupPrefix)
-	state := h2.newHandleState((*buffer.Buffer)(&h2.preformattedAttrs), false, "", prefix)
+	state := h2.newHandleState((*buffer.Buffer)(&h2.preformattedAttrs), false, "")
 	defer state.free()
+	state.prefix.WriteString(h.groupPrefix)
 	if len(h2.preformattedAttrs) > 0 {
 		state.sep = h.attrSep()
 	}
@@ -249,7 +251,7 @@ func (h *commonHandler) withGroup(name string) *commonHandler {
 }
 
 func (h *commonHandler) handle(r Record) error {
-	state := h.newHandleState(buffer.New(), true, "", nil)
+	state := h.newHandleState(buffer.New(), true, "")
 	defer state.free()
 	if h.json {
 		state.buf.WriteByte('{')
@@ -309,8 +311,6 @@ func (s *handleState) appendNonBuiltIns(r Record) {
 	}
 	// Attrs in Record -- unlike the built-in ones, they are in groups started
 	// from WithGroup.
-	s.prefix = buffer.New()
-	defer s.prefix.Free()
 	s.prefix.WriteString(s.h.groupPrefix)
 	s.openGroups()
 	r.Attrs(func(a Attr) bool {
@@ -352,13 +352,13 @@ var groupPool = sync.Pool{New: func() any {
 	return &s
 }}
 
-func (h *commonHandler) newHandleState(buf *buffer.Buffer, freeBuf bool, sep string, prefix *buffer.Buffer) handleState {
+func (h *commonHandler) newHandleState(buf *buffer.Buffer, freeBuf bool, sep string) handleState {
 	s := handleState{
 		h:       h,
 		buf:     buf,
 		freeBuf: freeBuf,
 		sep:     sep,
-		prefix:  prefix,
+		prefix:  buffer.New(),
 	}
 	if h.opts.ReplaceAttr != nil {
 		s.groups = groupPool.Get().(*[]string)
@@ -375,6 +375,7 @@ func (s *handleState) free() {
 		*gs = (*gs)[:0]
 		groupPool.Put(gs)
 	}
+	s.prefix.Free()
 }
 
 func (s *handleState) openGroups() {
diff --git a/src/log/slog/handler_test.go b/src/log/slog/handler_test.go
index fee611cf6a..741e86a826 100644
--- a/src/log/slog/handler_test.go
+++ b/src/log/slog/handler_test.go
@@ -262,11 +262,12 @@ func TestJSONAndTextHandlers(t *testing.T) {
 				return h.WithAttrs([]Attr{Int("p1", 1)}).
 					WithGroup("s1").
 					WithAttrs([]Attr{Int("p2", 2)}).
-					WithGroup("s2")
+					WithGroup("s2").
+					WithAttrs([]Attr{Int("p3", 3)})
 			},
 			attrs:    attrs,
-			wantText: "msg=message p1=1 s1.p2=2 s1.s2.a=one s1.s2.b=2",
-			wantJSON: `{"msg":"message","p1":1,"s1":{"p2":2,"s2":{"a":"one","b":2}}}`,
+			wantText: "msg=message p1=1 s1.p2=2 s1.s2.p3=3 s1.s2.a=one s1.s2.b=2",
+			wantJSON: `{"msg":"message","p1":1,"s1":{"p2":2,"s2":{"p3":3,"a":"one","b":2}}}`,
 		},
 		{
 			name:    "two with-groups",
@@ -326,6 +327,20 @@ func TestJSONAndTextHandlers(t *testing.T) {
 			wantText:  `source=handler_test.go:$LINE msg=message`,
 			wantJSON:  `{"source":{"function":"log/slog.TestJSONAndTextHandlers","file":"handler_test.go","line":$LINE},"msg":"message"}`,
 		},
+		{
+			name: "replace built-in with group",
+			replace: func(_ []string, a Attr) Attr {
+				if a.Key == TimeKey {
+					return Group(TimeKey, "mins", 3, "secs", 2)
+				}
+				if a.Key == LevelKey {
+					return Attr{}
+				}
+				return a
+			},
+			wantText: `time.mins=3 time.secs=2 msg=message`,
+			wantJSON: `{"time":{"mins":3,"secs":2},"msg":"message"}`,
+		},
 	} {
 		r := NewRecord(testTime, LevelInfo, "message", callerPC(2))
 		line := strconv.Itoa(r.source().Line)