diff --git a/Makefile b/Makefile
index bccf860490..e8f84225ec 100644
--- a/Makefile
+++ b/Makefile
@@ -216,6 +216,8 @@ tests/test.proto.pb: tests/test.proto
 SIMPLE_TESTS= \
   tests/test_def \
   tests/test_varint \
+  tests/test_pipeline \
+  tests/test_handlers
 
 SIMPLE_CXX_TESTS= \
   tests/test_cpp \
diff --git a/tests/test_handlers.c b/tests/test_handlers.c
index fb0564a783..36881fee7f 100644
--- a/tests/test_handlers.c
+++ b/tests/test_handlers.c
@@ -11,7 +11,11 @@
 #include <stdlib.h>
 #include <string.h>
 
-static bool startmsg(void *c, const void *hd) { return true; }
+static bool startmsg(void *c, const void *hd) {
+  UPB_UNUSED(c);
+  UPB_UNUSED(hd);
+  return true;
+}
 
 static void test_error() {
   upb_handlers *h = upb_handlers_new(GOOGLE_PROTOBUF_DESCRIPTORPROTO, NULL, &h);
@@ -33,6 +37,8 @@ static void test_error() {
 }
 
 int run_tests(int argc, char *argv[]) {
+  UPB_UNUSED(argc);
+  UPB_UNUSED(argv);
   test_error();
   return 0;
 }
diff --git a/tests/test_pipeline.c b/tests/test_pipeline.c
index d54d15c94a..7214ca58be 100644
--- a/tests/test_pipeline.c
+++ b/tests/test_pipeline.c
@@ -108,6 +108,8 @@ static void test_realloc() {
 }
 
 int run_tests(int argc, char *argv[]) {
+  UPB_UNUSED(argc);
+  UPB_UNUSED(argv);
   test_empty();
   test_only_initial();
   test_with_alloc_func();
diff --git a/upb/descriptor/reader.c b/upb/descriptor/reader.c
index e1b0c924e6..43bbdea35f 100644
--- a/upb/descriptor/reader.c
+++ b/upb/descriptor/reader.c
@@ -296,6 +296,7 @@ static bool enum_startmsg(void *closure, const void *hd) {
 }
 
 static bool enum_endmsg(void *closure, const void *hd, upb_status *status) {
+  UPB_UNUSED(hd);
   upb_descreader *r = closure;
   upb_enumdef *e = upb_downcast_enumdef_mutable(upb_descreader_last(r));
   if (upb_def_fullname(upb_descreader_last(r)) == NULL) {
diff --git a/upb/google/bridge.cc b/upb/google/bridge.cc
index 97a91eac9a..93864273b5 100644
--- a/upb/google/bridge.cc
+++ b/upb/google/bridge.cc
@@ -131,8 +131,8 @@ FieldDef* AddFieldDef(const goog::Message& m, const goog::FieldDescriptor* f,
                      : upb::FieldDef::ConvertDescriptorType(f->type()));
 
   if (weak_prototype) {
-    const string& name = weak_prototype->GetDescriptor()->full_name();
-    upb_f->set_subdef_name(name, &status);
+    upb_f->set_subdef_name(
+        weak_prototype->GetDescriptor()->full_name(), &status);
   } else {
     switch (upb_f->type()) {
       case UPB_TYPE_INT32:
diff --git a/upb/handlers-inl.h b/upb/handlers-inl.h
index 65f21a28f2..6b46b47bc7 100644
--- a/upb/handlers-inl.h
+++ b/upb/handlers-inl.h
@@ -303,8 +303,8 @@ inline Handlers::StringHandler BindHandler(
   template <>                                                                  \
   inline bool Handlers::SetValueHandler<vtype>(                                \
       const FieldDef *f,                                                       \
-      const typename ValueHandler<typename CanonicalType<vtype>::Type>::H &    \
-          handler) {                                                           \
+      const Handlers::utype ## Handler& handler) {                             \
+    assert(!handler.registered_);                                              \
     handler.registered_ = true;                                                \
     return upb_handlers_set##ltype(this, f, handler.handler_, handler.data_,   \
                                    handler.cleanup_);                          \
@@ -394,54 +394,63 @@ inline const MessageDef *Handlers::message_def() const {
 }
 inline bool Handlers::SetStartMessageHandler(
     const Handlers::StartMessageHandler &handler) {
+  assert(!handler.registered_);
   handler.registered_ = true;
   return upb_handlers_setstartmsg(this, handler.handler_, handler.data_,
                                   handler.cleanup_);
 }
 inline bool Handlers::SetEndMessageHandler(
     const Handlers::EndMessageHandler &handler) {
+  assert(!handler.registered_);
   handler.registered_ = true;
   return upb_handlers_setendmsg(this, handler.handler_, handler.data_,
                                 handler.cleanup_);
 }
 inline bool Handlers::SetStartStringHandler(const FieldDef *f,
                                             const StartStringHandler &handler) {
+  assert(!handler.registered_);
   handler.registered_ = true;
   return upb_handlers_setstartstr(this, f, handler.handler_, handler.data_,
                                   handler.cleanup_);
 }
 inline bool Handlers::SetEndStringHandler(const FieldDef *f,
                                           const EndFieldHandler &handler) {
+  assert(!handler.registered_);
   handler.registered_ = true;
   return upb_handlers_setendstr(this, f, handler.handler_, handler.data_,
                                 handler.cleanup_);
 }
 inline bool Handlers::SetStringHandler(const FieldDef *f,
                                        const StringHandler& handler) {
+  assert(!handler.registered_);
   handler.registered_ = true;
   return upb_handlers_setstring(this, f, handler.handler_, handler.data_,
                                 handler.cleanup_);
 }
 inline bool Handlers::SetStartSequenceHandler(
     const FieldDef *f, const StartFieldHandler &handler) {
+  assert(!handler.registered_);
   handler.registered_ = true;
   return upb_handlers_setstartseq(this, f, handler.handler_, handler.data_,
                                   handler.cleanup_);
 }
 inline bool Handlers::SetStartSubMessageHandler(
     const FieldDef *f, const StartFieldHandler &handler) {
+  assert(!handler.registered_);
   handler.registered_ = true;
   return upb_handlers_setstartsubmsg(this, f, handler.handler_, handler.data_,
                                      handler.cleanup_);
 }
 inline bool Handlers::SetEndSubMessageHandler(const FieldDef *f,
                                               const EndFieldHandler &handler) {
+  assert(!handler.registered_);
   handler.registered_ = true;
   return upb_handlers_setendsubmsg(this, f, handler.handler_, handler.data_,
                                    handler.cleanup_);
 }
 inline bool Handlers::SetEndSequenceHandler(const FieldDef *f,
                                             const EndFieldHandler &handler) {
+  assert(!handler.registered_);
   handler.registered_ = true;
   return upb_handlers_setendseq(this, f, handler.handler_, handler.data_,
                                 handler.cleanup_);
diff --git a/upb/handlers.h b/upb/handlers.h
index a80e401e74..21080463b4 100644
--- a/upb/handlers.h
+++ b/upb/handlers.h
@@ -116,13 +116,13 @@ class upb::Handlers {
     typedef Handler<bool(*)(void *, const void *, T)> H;
   };
 
-  typedef ValueHandler<upb_int32_t>::H     Int32Handler;
-  typedef ValueHandler<upb_int64_t>::H     Int64Handler;
-  typedef ValueHandler<upb_uint32_t>::H    UInt32Handler;
-  typedef ValueHandler<upb_uint64_t>::H    UInt64Handler;
-  typedef ValueHandler<float>::H           FloatHandler;
-  typedef ValueHandler<double>::H          DoubleHandler;
-  typedef ValueHandler<bool>::H            BoolHandler;
+  typedef ValueHandler<int32_t>::H     Int32Handler;
+  typedef ValueHandler<int64_t>::H     Int64Handler;
+  typedef ValueHandler<uint32_t>::H    UInt32Handler;
+  typedef ValueHandler<uint64_t>::H    UInt64Handler;
+  typedef ValueHandler<float>::H       FloatHandler;
+  typedef ValueHandler<double>::H      DoubleHandler;
+  typedef ValueHandler<bool>::H        BoolHandler;
 
   // Any function pointer can be converted to this and converted back to its
   // correct type.
@@ -470,8 +470,14 @@ template <class T> class Handler {
 
   Handler(FuncPtr h, void *d, void (*c)(void *))
       : handler_(h), data_(d), cleanup_(c), registered_(false) {}
-  Handler(const Handler&);
   void operator=(const Handler&);
+#ifdef UPB_CXX11
+  // C++98 doesn't support binding a const ref to a temporary, at least
+  // according to Clang.  It is still intended that users NOT create instances
+  // of this object via this copy constructor, and any attempts to register
+  // such an object more than once will assert-fail.
+  Handler(const Handler&);
+#endif
 
   FuncPtr handler_;
   void *data_;