diff --git a/include/nonstd/expected.hpp b/include/nonstd/expected.hpp
index fdfb432..0217b9b 100644
--- a/include/nonstd/expected.hpp
+++ b/include/nonstd/expected.hpp
@@ -2165,7 +2165,11 @@ class expected<void, E>
 
 // x.x.4.6 expected<>: comparison operators
 
-template< typename T1, typename E1, typename T2, typename E2 >
+template< typename T1, typename E1, typename T2, typename E2
+    nsel_REQUIRES_T(
+        !std::is_void<T1>::value && !std::is_void<T2>::value
+    )
+>
 constexpr bool operator==( expected<T1,E1> const & x, expected<T2,E2> const & y )
 {
     return bool(x) != bool(y) ? false : bool(x) == false ? x.error() == y.error() : *x == *y;
@@ -2213,13 +2217,21 @@ constexpr bool operator>=( expected<T,E> const & x, expected<T,E> const & y )
 
 // x.x.4.7 expected: comparison with T
 
-template< typename T1, typename E1, typename T2 >
+template< typename T1, typename E1, typename T2
+    nsel_REQUIRES_T(
+        !std::is_void<T1>::value
+    )
+>
 constexpr bool operator==( expected<T1,E1> const & x, T2 const & v )
 {
     return bool(x) ? *x == v : false;
 }
 
-template< typename T1, typename E1, typename T2 >
+template< typename T1, typename E1, typename T2
+    nsel_REQUIRES_T(
+        !std::is_void<T1>::value
+    )
+>
 constexpr bool operator==(T2 const & v, expected<T1,E1> const & x )
 {
     return bool(x) ? v == *x : false;
diff --git a/test/expected.t.cpp b/test/expected.t.cpp
index 2f70046..fe43e25 100644
--- a/test/expected.t.cpp
+++ b/test/expected.t.cpp
@@ -1838,6 +1838,24 @@ nonstd::unexpected_type<MyConstMemberNonMoveableObject> create_nonmoveable()
 
 } // namespace issue_50
 
+namespace issue_51 {
+
+int compare_equal_with_expected_void()
+{
+    auto ev1 = nonstd::expected<void, int>{};
+    auto ev2 = nonstd::expected<void, int>{};
+    return ev1 == ev2;
+}
+
+int compare_not_equal_with_expected_void()
+{
+    auto ev1 = nonstd::expected<void, int>{};
+    auto ev2 = nonstd::expected<void, int>{};
+    return ev1 != ev2;
+}
+
+} // namespace issue_51
+
 // -----------------------------------------------------------------------
 //  using as optional