diff --git a/src/Json.c b/src/Json.c
index 85654c5..e02f08c 100644
--- a/src/Json.c
+++ b/src/Json.c
@@ -372,7 +372,7 @@ JsonEncodeString(const char *str, FILE * out)
                  */
                 if (c <= 0x001F)
                 {
-                    printf("\\u%04x", c);
+                    fprintf(out, "\\u%04x", c);
                 }
                 else
                 {