diff --git a/pkg/util/framer/framer.go b/pkg/util/framer/framer.go
index 1e886e818f..615d07de1c 100644
--- a/pkg/util/framer/framer.go
+++ b/pkg/util/framer/framer.go
@@ -145,6 +145,7 @@ func (r *jsonFrameReader) Read(data []byte) (int, error) {
 
 	// RawMessage#Unmarshal appends to data - we reset the slice down to 0 and will either see
 	// data written to data, or be larger than data and a different array.
+	n := len(data)
 	m := json.RawMessage(data[:0])
 	if err := r.decoder.Decode(&m); err != nil {
 		return 0, err
@@ -153,7 +154,7 @@ func (r *jsonFrameReader) Read(data []byte) (int, error) {
 	// If capacity of data is less than length of the message, decoder will allocate a new slice
 	// and set m to it, which means we need to copy the partial result back into data and preserve
 	// the remaining result for subsequent reads.
-	if n := cap(data); len(m) > n {
+	if len(m) > n {
 		data = append(data[0:0], m[:n]...)
 		r.remaining = m[n:]
 		return n, io.ErrShortBuffer