diff --git a/include/groov/write.hpp b/include/groov/write.hpp
index 45cc893..25ad5db 100644
--- a/include/groov/write.hpp
+++ b/include/groov/write.hpp
@@ -118,9 +118,9 @@ auto write(Spec const &s) -> async::sender auto {
                                   all_fields_per_reg_t,
                                   written_fields_per_reg_t>;
 
-    using field_masks_t = boost::mp11::mp_transform<detail::compute_mask_t,
-                                                    typename Spec::value_t,
-                                                    written_fields_per_reg_t>;
+    using field_masks_t =
+        boost::mp11::mp_transform<detail::compute_mask_t,
+                                  typename Spec::value_t, fields_per_reg_t>;
 
     detail::check_read_only<typename Spec::bus_t, fields_per_reg_t>();
     detail::check_rmw<typename Spec::bus_t, unwritten_fields_per_reg_t,
diff --git a/test/test.cpp b/test/test.cpp
index 7159729..805a2ae 100644
--- a/test/test.cpp
+++ b/test/test.cpp
@@ -193,14 +193,14 @@ TEST_CASE("test_bus write function", "[test]") {
         write_value = get<std::uint32_t>(value).value_or(0);
     });
 
-    groov::sync_write(grp0("reg0"_r = 0x76));
+    groov::sync_write(grp0("reg0"_r = 0x10325476u));
 
     CHECK(data0 == 0xa5a5'a5a5u);
     CHECK(my_bus::num_reads == 0);
     CHECK(my_bus::num_writes == 0);
     CHECK(write_call_count == 1);
     CHECK(write_addr == &data0);
-    CHECK(write_value == 0xbabefa76u);
+    CHECK(write_value == 0x10325476u);
     auto v = groov::test::get_value<G0>("reg0"_f);
     REQUIRE(v);
     CHECK(*v == 0xbabefaceu);
diff --git a/test/write.cpp b/test/write.cpp
index 7f0858b..2f82bab 100644
--- a/test/write.cpp
+++ b/test/write.cpp
@@ -15,6 +15,7 @@
 
 #include <array>
 #include <cstdint>
+#include <limits>
 
 namespace {
 struct bus {
@@ -549,3 +550,74 @@ TEST_CASE("write a field in a register containing WO fields which won't be "
     CHECK(groov::write(grp_be("reg4.field0"_r = 1)) | async::sync_wait());
     CHECK(data3 == 42);
 }
+
+namespace {
+struct rmw_check_bus {
+    static inline std::uint32_t expected_mask{};
+
+    template <stdx::ct_string, auto Mask, auto IdMask, auto IdValue>
+    static auto write(auto addr, auto value) -> async::sender auto {
+        CHECK((Mask | IdMask) == expected_mask);
+        return async::just_result_of([=] {
+            auto prev = *addr & ~(Mask | IdMask);
+            *addr = prev | value | IdValue;
+        });
+    }
+
+    template <stdx::ct_string, auto Mask>
+    static auto read(auto addr) -> async::sender auto {
+        return async::just_result_of([=] { return *addr; });
+    }
+};
+
+std::uint32_t rmw_check_data{};
+using rmw_check_R = groov::reg<"r", std::uint32_t, &rmw_check_data,
+                               groov::w::replace, F0, F1, F2>;
+
+using rmw_check_G = groov::group<"group", rmw_check_bus, rmw_check_R>;
+constexpr auto rmw_check_grp = rmw_check_G{};
+} // namespace
+
+TEST_CASE("writing a register that is not covered by fields does not RMW",
+          "[write]") {
+    using namespace groov::literals;
+    rmw_check_bus::expected_mask = 0xffff'ffffu;
+    rmw_check_data = 0;
+    CHECK(groov::write(rmw_check_grp("r"_r = 0xa5a5u)) | async::sync_wait());
+    CHECK(rmw_check_data == 0xa5a5u);
+}
+
+TEST_CASE("writing register fields in a register that is not covered by fields "
+          "incurs RMW",
+          "[write]") {
+    using namespace groov::literals;
+    rmw_check_bus::expected_mask = 0xffu;
+    rmw_check_data = 0;
+    CHECK(
+        groov::write(rmw_check_grp("r.field0"_f = 0b1u, "r.field1"_f = 0b1010u,
+                                   "r.field2"_f = 0b110u)) |
+        async::sync_wait());
+    CHECK(rmw_check_data == 0b110'1010'1u);
+}
+
+namespace {
+using F_overlap = groov::field<"f_overlap", std::uint8_t, 3, 0>;
+
+std::uint32_t overlap_data{};
+using R_overlap = groov::reg<"r", std::uint32_t, &overlap_data,
+                             groov::w::replace, F0, F_overlap>;
+
+using G_overlap = groov::group<"group", bus, R_overlap>;
+constexpr auto overlap_grp = G_overlap{};
+} // namespace
+
+TEST_CASE("overlapping writes: last one takes priority", "[write]") {
+    using namespace groov::literals;
+    overlap_data = 0xffff'ffffu;
+    CHECK(sync_write(overlap_grp("r.f_overlap"_r = 0, "r.field0"_f = 1)));
+    CHECK(overlap_data == 0xffff'fff1u);
+
+    overlap_data = 0xffff'ffffu;
+    CHECK(sync_write(overlap_grp("r.field0"_f = 1, "r.f_overlap"_r = 0)));
+    CHECK(overlap_data == 0xffff'fff0u);
+}