diff --git a/include/gsl.h b/include/gsl.h
index 1357d76..b78c6e2 100644
--- a/include/gsl.h
+++ b/include/gsl.h
@@ -162,7 +162,11 @@ private:
 template<class T>
 class maybe_null_dbg
 {
+    template<class U>
+    friend class maybe_null_dbg;
 public:
+    static_assert(std::is_constructible<T, std::nullptr_t>::value, "maybe_null's template parameter must be constructible from nullptr");
+
     maybe_null_dbg() : ptr_(nullptr), tested_(false) {}
 
     maybe_null_dbg(const T& p) : ptr_(p), tested_(false) {}
@@ -202,8 +206,10 @@ public:
 
     bool operator==(const T& rhs) const { tested_ = true; return ptr_ == rhs; }
     bool operator!=(const T& rhs) const { return !(*this == rhs); }
-    bool operator==(const maybe_null_dbg& rhs) const { tested_ = true; rhs.tested_ = true; return ptr_ == rhs.ptr_; }
-    bool operator!=(const maybe_null_dbg& rhs) const { return !(*this == rhs); }
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    bool operator==(const maybe_null_dbg<U>& rhs) const { tested_ = true; rhs.tested_ = true; return ptr_ == rhs.ptr_; }
+    template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
+    bool operator!=(const maybe_null_dbg<U>& rhs) const { return !(*this == rhs); }
 
     T get() const {
         fail_fast_assert(tested_);
@@ -217,8 +223,6 @@ public:
     T operator->() const { return get(); }
 
 private:
-    const size_t ptee_size_ = sizeof(*ptr_);  // T must be a pointer type
-
     // unwanted operators...pointers only point to single objects!
     // TODO ensure all arithmetic ops on this type are unavailable
     maybe_null_dbg<T>& operator++() = delete;
@@ -238,6 +242,8 @@ template<class T>
 class maybe_null_ret
 {
 public:
+    static_assert(std::is_constructible<T, std::nullptr_t>::value, "maybe_null's template parameter must be constructible from nullptr");
+
     maybe_null_ret() : ptr_(nullptr) {}
     maybe_null_ret(std::nullptr_t) : ptr_(nullptr) {}
     maybe_null_ret(const T& p) : ptr_(p) {}
@@ -280,7 +286,6 @@ private:
     maybe_null_ret<T>& operator-(size_t) = delete;
     maybe_null_ret<T>& operator-=(size_t) = delete;
 
-    const size_t ptee_size_ = sizeof(*ptr_);  // T must be a pointer type
     T ptr_;
 };
 
diff --git a/tests/maybenull_tests.cpp b/tests/maybenull_tests.cpp
index 0a9d891..e1244fd 100644
--- a/tests/maybenull_tests.cpp
+++ b/tests/maybenull_tests.cpp
@@ -241,6 +241,20 @@ SUITE(MaybeNullTests)
         // Make sure we no longer throw here
         CHECK(p1.get() != nullptr);
     }
+
+    TEST(TestMaybeNullPtrT)
+    {
+        maybe_null<std::nullptr_t> p1;
+        maybe_null<std::nullptr_t> p2;
+
+        CHECK_THROW(p1.get(), fail_fast);
+
+        CHECK(p1 == p2);
+
+        // Make sure we no longer throw here
+        CHECK(p1.get() == nullptr);
+        CHECK(p2.get() == nullptr);
+    }
 }
 
 int main(int, const char *[])