diff --git a/README.md b/README.md
index 9b83e7b..a24307d 100644
--- a/README.md
+++ b/README.md
@@ -304,14 +304,14 @@ auto syntax = R"(
 
 Rules rules = {
     {
-        "NAME", usr([](const char* s, size_t n, SemanticValues& sv, any& c) {
+        "NAME", usr([](const char* s, size_t n, SemanticValues& sv, any& c) -> size_t {
             static vector<string> names = { "PEG", "BNF" };
-            for (const auto& n: names) {
-                if (n.size() <= n && !n.compare(0, n.size(), s, n.size())) {
-                    return success(n.size());
+            for (const auto& name: names) {
+                if (name.size() <= n && !name.compare(0, name.size(), s, name.size())) {
+                    return name.size();
                 }
             }
-            return fail(s);
+            return -1;
         })
     },
     {
diff --git a/peglib.h b/peglib.h
index cbd8a5e..a634209 100644
--- a/peglib.h
+++ b/peglib.h
@@ -284,7 +284,7 @@ any call(F fn, Args&&... args) {
 /*
  * Predicate
  */
-typedef std::function<bool(const char* s, size_t n, const any& val, const any& dt)> Predicate;
+typedef std::function<bool (const char* s, size_t n, const any& val, const any& dt)> Predicate;
 #endif
 
 class Action
@@ -902,7 +902,7 @@ public:
     std::shared_ptr<Ope> ope_;
 };
 
-typedef std::function<size_t(const char* s, size_t n, SemanticValues& sv, any& dt)> Parser;
+typedef std::function<size_t (const char* s, size_t n, SemanticValues& sv, any& dt)> Parser;
 
 class User : public Ope
 {
@@ -916,7 +916,7 @@ public:
 
     void accept(Visitor& v) override;
 
-    std::function<size_t(const char* s, size_t n, SemanticValues& sv, any& dt)> fn_;
+    std::function<size_t (const char* s, size_t n, SemanticValues& sv, any& dt)> fn_;
 };
 
 class WeakHolder : public Ope
diff --git a/test/test.cc b/test/test.cc
index 111a7b4..6374af5 100644
--- a/test/test.cc
+++ b/test/test.cc
@@ -613,6 +613,32 @@ TEST_CASE("Left recursive with empty string test", "[left recursive]")
     REQUIRE(parser == false);
 }
 
+TEST_CASE("User rule test", "[user rule]")
+{
+    auto syntax = " ROOT <- _ 'Hello' _ NAME '!' _ ";
+
+    Rules rules = {
+        {
+            "NAME", usr([](const char* s, size_t n, SemanticValues& sv, any& c) -> size_t {
+                static vector<string> names = { "PEG", "BNF" };
+                for (const auto& name: names) {
+                    if (name.size() <= n && !name.compare(0, name.size(), s, name.size())) {
+                        return name.size();
+                    }
+                }
+                return -1;
+            })
+        },
+        {
+            "~_", zom(cls(" \t\r\n"))
+        }
+    };
+
+    peg g = peg(syntax, rules);
+
+    REQUIRE(g.parse(" Hello BNF! ") == true);
+}
+
 bool exact(Grammar& g, const char* d, const char* s) {
     auto n = strlen(s);
     auto r = g[d].parse(s, n);