diff --git a/src/json_lib.cpp b/src/json_lib.cpp
index 3948c9a..f3d7dc8 100644
--- a/src/json_lib.cpp
+++ b/src/json_lib.cpp
@@ -115,6 +115,12 @@ std::string json::var_generate(var& value) {
 }
 
 std::string json::vector_generate(nas_vec& vect) {
+    // avoid stackoverflow
+    if (vect.printed) {
+        error_info() += "json::stringify: get vector containing itself\n";
+        return "undefined";
+    }
+    vect.printed = true;
     std::string out = "[";
     for(auto& i : vect.elems) {
         out += var_generate(i) + ",";
@@ -123,10 +129,17 @@ std::string json::vector_generate(nas_vec& vect) {
         out.pop_back();
     }
     out += "]";
+    vect.printed = false;
     return out;
 }
 
 std::string json::hash_generate(nas_hash& hash) {
+    // avoid stackoverflow
+    if (hash.printed) {
+        error_info() += "json::stringify: get hash containing itself\n";
+        return "undefined";
+    }
+    hash.printed = true;
     std::string out = "{";
     for(auto& i : hash.elems) {
         out += "\"" + i.first + "\":";
@@ -136,6 +149,7 @@ std::string json::hash_generate(nas_hash& hash) {
         out.pop_back();
     }
     out += "}";
+    hash.printed = false;
     return out;
 }
 
diff --git a/test/json.nas b/test/json.nas
index 0e24d05..4d0aa2e 100644
--- a/test/json.nas
+++ b/test/json.nas
@@ -66,6 +66,20 @@ test_func(json.stringify({
 test_func("");
 println();
 
+func {
+    var a = {};
+    a.a = a;
+
+    var b = [];
+    append(b, b);
+
+    println(json.stringify(a));
+    println(json.get_error());
+    println(json.stringify(b));
+    println(json.get_error());
+    println();
+}();
+
 var test_json = func(json) {
     var bar = process_bar.high_resolution_bar(30);
     var tmp = [