diff --git a/docs/changelog.rst b/docs/changelog.rst
index 7cf26e107..c9e988b1d 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -8,10 +8,11 @@ Changelog
 * Redesigned virtual call mechanism and user-facing syntax (breaking change!)
 * Prevent implicit conversion of floating point values to integral types in
   function arguments
-* Transparent conversion of sparse and dense Eigen data types
+* Transparent conversion of sparse and dense Eigen matrices and vectors
 * ``std::vector<>`` type bindings analogous to Boost.Python's ``indexing_suite``
 * Fixed incorrect default return value policy for functions returning a shared
   pointer
+* Don't allow registering a type via ``class_`` twice
 * Don't allow casting a ``None`` value into a C++ lvalue reference
 * Fixed a crash in ``enum_::operator==`` that was triggered by the ``help()`` command
 * Improved detection of whether or not custom C++ types can be copy/move-constructed
diff --git a/example/issues.cpp b/example/issues.cpp
index e1647081f..dfe20fff8 100644
--- a/example/issues.cpp
+++ b/example/issues.cpp
@@ -131,4 +131,11 @@ void init_issues(py::module &m) {
 	    .def("f", &A::f);
 
 	 m2.def("call_f", call_f);
+
+    try {
+        py::class_<Placeholder>(m2, "Placeholder");
+        throw std::logic_error("Expected an exception!");
+    } catch (std::runtime_error &e) {
+        /* All good */
+    }
 }
diff --git a/include/pybind11/pybind11.h b/include/pybind11/pybind11.h
index 964aea90e..4ffe1108f 100644
--- a/include/pybind11/pybind11.h
+++ b/include/pybind11/pybind11.h
@@ -520,6 +520,14 @@ protected:
             }
         }
 
+        auto &internals = get_internals();
+        auto tindex = std::type_index(*(rec->type));
+
+        if (internals.registered_types_cpp.find(tindex) !=
+            internals.registered_types_cpp.end())
+            pybind11_fail("generic_type: type \"" + std::string(rec->name) +
+                          "\" is already registered!");
+
         object type_holder(PyType_Type.tp_alloc(&PyType_Type, 0), false);
         object name(PYBIND11_FROM_STRING(rec->name), false);
         auto type = (PyHeapTypeObject*) type_holder.ptr();
@@ -528,12 +536,11 @@ protected:
             pybind11_fail("generic_type: unable to create type object!");
 
         /* Register supplemental type information in C++ dict */
-        auto &internals = get_internals();
         detail::type_info *tinfo = new detail::type_info();
         tinfo->type = (PyTypeObject *) type;
         tinfo->type_size = rec->type_size;
         tinfo->init_holder = rec->init_holder;
-        internals.registered_types_cpp[std::type_index(*(rec->type))] = tinfo;
+        internals.registered_types_cpp[tindex] = tinfo;
         internals.registered_types_py[type] = tinfo;
 
         object scope_module;