diff --git a/qobject/json-parser.c b/qobject/json-parser.c
index 273f448a52..63e9229f1c 100644
--- a/qobject/json-parser.c
+++ b/qobject/json-parser.c
@@ -144,7 +144,8 @@ static QString *parse_string(JSONParserContext *ctxt, JSONToken *token)
 
     while (*ptr != quote) {
         assert(*ptr);
-        if (*ptr == '\\') {
+        switch (*ptr) {
+        case '\\':
             beg = ptr++;
             switch (*ptr++) {
             case '"':
@@ -205,7 +206,14 @@ static QString *parse_string(JSONParserContext *ctxt, JSONToken *token)
                 parse_error(ctxt, token, "invalid escape sequence in string");
                 goto out;
             }
-        } else {
+            break;
+        case '%':
+            if (ctxt->ap) {
+                parse_error(ctxt, token, "can't interpolate into string");
+                goto out;
+            }
+            /* fall through */
+        default:
             cp = mod_utf8_codepoint(ptr, 6, &end);
             if (cp < 0) {
                 parse_error(ctxt, token, "invalid UTF-8 sequence in string");
diff --git a/tests/check-qjson.c b/tests/check-qjson.c
index 936258ddd4..a1854573de 100644
--- a/tests/check-qjson.c
+++ b/tests/check-qjson.c
@@ -1037,16 +1037,13 @@ static void interpolation_unknown(void)
 
 static void interpolation_string(void)
 {
-    QLitObject decoded = QLIT_QLIST(((QLitObject[]){
-            QLIT_QSTR("%s"),
-            QLIT_QSTR("eins"),
-            {}}));
-    QObject *qobj;
-
-    /* Dangerous misfeature: % is silently ignored in strings */
-    qobj = qobject_from_jsonf_nofail("['%s', %s]", "eins", "zwei");
-    g_assert(qlit_equal_qobject(&decoded, qobj));
-    qobject_unref(qobj);
+    if (g_test_subprocess()) {
+        qobject_from_jsonf_nofail("['%s', %s]", "eins", "zwei");
+    }
+    g_test_trap_subprocess(NULL, 0, 0);
+    g_test_trap_assert_failed();
+    g_test_trap_assert_stderr("*Unexpected error*"
+                              "can't interpolate into string*");
 }
 
 static void simple_dict(void)