diff --git a/include/qpdf/JSON.hh b/include/qpdf/JSON.hh
index 3ff714ae..ef820b66 100644
--- a/include/qpdf/JSON.hh
+++ b/include/qpdf/JSON.hh
@@ -374,16 +374,7 @@ class JSON
         std::map<std::string, JSON> members;
         std::set<std::string> parsed_keys;
     };
-    struct JSON_array: public JSON_value
-    {
-        JSON_array() :
-            JSON_value(vt_array)
-        {
-        }
-        ~JSON_array() override = default;
-        void write(Pipeline*, size_t depth) const override;
-        std::vector<JSON> elements;
-    };
+    struct JSON_array;
     struct JSON_string: public JSON_value
     {
         JSON_string(std::string const& utf8);
@@ -455,4 +446,15 @@ class JSON
     std::shared_ptr<Members> m;
 };
 
+struct JSON::JSON_array: public JSON_value
+{
+    JSON_array() :
+        JSON_value(vt_array)
+    {
+    }
+    ~JSON_array() override = default;
+    void write(Pipeline*, size_t depth) const override;
+    std::vector<JSON> elements;
+};
+
 #endif // JSON_HH