diff --git a/libqpdf/JSON.cc b/libqpdf/JSON.cc
index c656bb1..a45dbd2 100644
--- a/libqpdf/JSON.cc
+++ b/libqpdf/JSON.cc
@@ -181,6 +181,9 @@ JSON::encode_string(std::string const& str)
           case '\b':
             result += "\\b";
             break;
+          case '\f':
+            result += "\\f";
+            break;
           case '\n':
             result += "\\n";
             break;
diff --git a/qpdf/qtest/qpdf/json-outlines-with-actions.out b/qpdf/qtest/qpdf/json-outlines-with-actions.out
index 9755d0b..bfc67cf 100644
--- a/qpdf/qtest/qpdf/json-outlines-with-actions.out
+++ b/qpdf/qtest/qpdf/json-outlines-with-actions.out
@@ -1653,8 +1653,8 @@
     "99 0 R": 46,
     "trailer": {
       "/ID": [
-        "Õ+\u000c\u0017Â\u0016Pib®gC¯ì&\u000f",
-        "Õ+\u000c\u0017Â\u0016Pib®gC¯ì&\u000f"
+        "Õ+\f\u0017Â\u0016Pib®gC¯ì&\u000f",
+        "Õ+\f\u0017Â\u0016Pib®gC¯ì&\u000f"
       ],
       "/Root": "1 0 R",
       "/Size": 109
diff --git a/qpdf/qtest/qpdf/json-outlines-with-old-root-dests.out b/qpdf/qtest/qpdf/json-outlines-with-old-root-dests.out
index af3ce99..2d4a81d 100644
--- a/qpdf/qtest/qpdf/json-outlines-with-old-root-dests.out
+++ b/qpdf/qtest/qpdf/json-outlines-with-old-root-dests.out
@@ -1651,8 +1651,8 @@
     "99 0 R": 45,
     "trailer": {
       "/ID": [
-        "Õ+\u000c\u0017Â\u0016Pib®gC¯ì&\u000f",
-        "Õ+\u000c\u0017Â\u0016Pib®gC¯ì&\u000f"
+        "Õ+\f\u0017Â\u0016Pib®gC¯ì&\u000f",
+        "Õ+\f\u0017Â\u0016Pib®gC¯ì&\u000f"
       ],
       "/Root": "1 0 R",
       "/Size": 108