diff --git a/src/encoding/pem/pem.go b/src/encoding/pem/pem.go
index 4b4f7490210..951e9163571 100644
--- a/src/encoding/pem/pem.go
+++ b/src/encoding/pem/pem.go
@@ -193,30 +193,29 @@ type lineBreaker struct {
 var nl = []byte{'\n'}
 
 func (l *lineBreaker) Write(b []byte) (n int, err error) {
-	if l.used+len(b) < pemLineLength {
-		copy(l.line[l.used:], b)
-		l.used += len(b)
-		return len(b), nil
+	var n1 int
+	for len(b) > 0 {
+		if l.used+len(b) < pemLineLength {
+			copy(l.line[l.used:], b)
+			l.used += len(b)
+			n += len(b)
+			return
+		}
+		_, err = l.out.Write(l.line[0:l.used])
+		excess := pemLineLength - l.used
+		l.used = 0
+		n1, err = l.out.Write(b[0:excess])
+		n += n1
+		if err != nil {
+			return n, err
+		}
+		_, err = l.out.Write(nl)
+		if err != nil {
+			return
+		}
+		b = b[excess:]
 	}
-
-	n, err = l.out.Write(l.line[0:l.used])
-	if err != nil {
-		return
-	}
-	excess := pemLineLength - l.used
-	l.used = 0
-
-	n, err = l.out.Write(b[0:excess])
-	if err != nil {
-		return
-	}
-
-	n, err = l.out.Write(nl)
-	if err != nil {
-		return
-	}
-
-	return l.Write(b[excess:])
+	return
 }
 
 func (l *lineBreaker) Close() (err error) {
diff --git a/src/encoding/pem/pem_test.go b/src/encoding/pem/pem_test.go
index 56a7754b220..b0920751aea 100644
--- a/src/encoding/pem/pem_test.go
+++ b/src/encoding/pem/pem_test.go
@@ -233,6 +233,34 @@ func TestLineBreaker(t *testing.T) {
 			t.Errorf("#%d: (byte by byte) got:%s want:%s", i, got, test.out)
 		}
 	}
+
+	t.Run("SmallBuffer", func(t *testing.T) {
+		buf := new(strings.Builder)
+		breaker := lineBreaker{out: buf}
+		input := bytes.Repeat([]byte("a"), 10) // Less than pemLineLength
+
+		written, err := breaker.Write(input)
+		if err != nil {
+			t.Fatalf("Write failed: %v", err)
+		}
+		if written != len(input) {
+			t.Errorf("Expected to write %d bytes, wrote %d bytes", len(input), written)
+		}
+	})
+
+	t.Run("LargeBuffer", func(t *testing.T) {
+		buf := new(strings.Builder)
+		breaker := lineBreaker{out: buf}
+		input := bytes.Repeat([]byte("a"), 200) // More than pemLineLength
+
+		written, err := breaker.Write(input)
+		if err != nil {
+			t.Fatalf("Write failed: %v", err)
+		}
+		if written != len(input) {
+			t.Errorf("Expected to write %d bytes, wrote %d bytes", len(input), written)
+		}
+	})
 }
 
 func TestFuzz(t *testing.T) {