diff --git a/src/pack_unpack.c b/src/pack_unpack.c
index eb15b17..5001764 100644
--- a/src/pack_unpack.c
+++ b/src/pack_unpack.c
@@ -9,6 +9,7 @@
 #include <string.h>
 #include <jansson.h>
 #include "jansson_private.h"
+#include "utf.h"
 
 typedef struct {
     const char *start;
@@ -110,13 +111,18 @@ static json_t *pack_object(scanner_t *s, va_list *ap)
             goto error;
         }
 
+        if(!utf8_check_string(key, -1)) {
+            set_error(s, "<args>", "Invalid UTF-8 in object key");
+            goto error;
+        }
+
         next_token(s);
 
         value = pack(s, ap);
         if(!value)
             goto error;
 
-        if(json_object_set_new(object, key, value)) {
+        if(json_object_set_new_nocheck(object, key, value)) {
             set_error(s, "<internal>", "Unable to add key \"%s\"", key);
             goto error;
         }
@@ -178,7 +184,11 @@ static json_t *pack(scanner_t *s, va_list *ap)
                 set_error(s, "<args>", "NULL string argument");
                 return NULL;
             }
-            return json_string(str);
+            if(!utf8_check_string(str, -1)) {
+                set_error(s, "<args>", "Invalid UTF-8 string");
+                return NULL;
+            }
+            return json_string_nocheck(str);
         }
 
         case 'n': /* null */
diff --git a/test/suites/api/test_pack.c b/test/suites/api/test_pack.c
index add5841..ccab051 100644
--- a/test/suites/api/test_pack.c
+++ b/test/suites/api/test_pack.c
@@ -208,14 +208,25 @@ int main()
         fail("json_pack failed to catch object as key");
     check_error("Expected format 's', got '{'", "<format>", 1, 3, 3);
 
-
+    /* Complex object */
     if(json_pack_ex(&error, 0, "{ s: {},  s:[ii{} }", "foo", "bar", 12, 13))
         fail("json_pack failed to catch missing ]");
     check_error("Unexpected format character '}'", "<format>", 1, 19, 19);
 
+    /* Complex array */
     if(json_pack_ex(&error, 0, "[[[[[   [[[[[  [[[[ }]]]] ]]]] ]]]]]"))
         fail("json_pack failed to catch extra }");
     check_error("Unexpected format character '}'", "<format>", 1, 21, 21);
 
+    /* Invalid UTF-8 in object key */
+    if(json_pack_ex(&error, 0, "{s:i}", "\xff\xff", 42))
+        fail("json_pack failed to catch invalid UTF-8 in an object key");
+    check_error("Invalid UTF-8 in object key", "<args>", 1, 2, 2);
+
+    /* Invalid UTF-8 in a string */
+    if(json_pack_ex(&error, 0, "{s:s}", "foo", "\xff\xff"))
+        fail("json_pack failed to catch invalid UTF-8 in a string");
+    check_error("Invalid UTF-8 string", "<args>", 1, 4, 4);
+
     return 0;
 }