diff --git a/test/scan-test.cc b/test/scan-test.cc
index 803ba0697850..f78d72ca35c5 100644
--- a/test/scan-test.cc
+++ b/test/scan-test.cc
@@ -97,7 +97,10 @@ template <> struct scanner<num> {
 
   auto parse(scan_parse_context& ctx) -> scan_parse_context::iterator {
     auto it = ctx.begin(), end = ctx.end();
-    if (it != end && *it == 'x') hex = true;
+    if (it != end && *it == 'x') {
+      hex = true;
+      ++it;
+    }
     if (it != end && *it != '}') throw_format_error("invalid format");
     return it;
   }
@@ -111,9 +114,8 @@ template <> struct scanner<num> {
 }  // namespace fmt
 
 TEST(scan_test, read_custom) {
-  auto input = "42";
   auto n = num();
-  fmt::scan(input, "{:}", n);
+  fmt::scan("42", "{}", n);
   EXPECT_EQ(n.value, 42);
 }
 
diff --git a/test/scan.h b/test/scan.h
index 1ef94f41f0a7..54714313d97b 100644
--- a/test/scan.h
+++ b/test/scan.h
@@ -607,8 +607,9 @@ struct scan_handler {
     return 0;
   }
 
-  void on_replacement_field(int arg_id, const char*) {
+  void on_replacement_field(int arg_id, const char* begin) {
     scan_arg arg = scan_ctx_.arg(arg_id);
+    if (arg.scan_custom(begin, parse_ctx_, scan_ctx_)) return;
     auto it = scan_ctx_.begin();
     while (it != sentinel() && is_whitespace(*it)) ++it;
     scan_ctx_.advance_to(arg.visit(default_arg_scanner{it}));