diff --git a/test/mp/test/foo.capnp b/test/mp/test/foo.capnp
index 31736452..ba8c6993 100644
--- a/test/mp/test/foo.capnp
+++ b/test/mp/test/foo.capnp
@@ -15,7 +15,6 @@ interface FooInterface $Proxy.wrap("mp::test::FooImplementation") {
     add @0 (a :Int32, b :Int32) -> (result :Int32);
     addOut @19 (a :Int32, b :Int32) -> (ret :Int32);
     addInOut @20 (x :Int32, sum :Int32) -> (sum :Int32);
-    mapSize @1 (map :List(Pair(Text, Text))) -> (result :Int32);
     pass @2 (arg :FooStruct) -> (result :FooStruct);
     raise @3 (arg :FooStruct) -> (error :FooStruct $Proxy.exception("mp::test::FooStruct"));
     initThreadMap @4 (threadMap: Proxy.ThreadMap) -> (threadMap :Proxy.ThreadMap);
@@ -30,7 +29,7 @@ interface FooInterface $Proxy.wrap("mp::test::FooImplementation") {
     passMessage @13 (arg :FooMessage) -> (result :FooMessage);
     passMutable @14 (arg :FooMutable) -> (arg :FooMutable);
     passEnum @15 (arg :Int32) -> (result :Int32);
-    passDouble @23 (arg :Float64) -> (result :Float64);
+    passDouble @1 (arg :Float64) -> (result :Float64);
     passFn @16 (context :Proxy.Context, fn :FooFn) -> (result :Int32);
     callFn @17 () -> ();
     callFnAsync @18 (context :Proxy.Context) -> ();
@@ -55,10 +54,11 @@ interface FooFn $Proxy.wrap("ProxyCallback<std::function<int()>>") {
 struct FooStruct $Proxy.wrap("mp::test::FooStruct") {
     name @0 :Text;
     setInt @1 :List(Int32) $Proxy.name("set_int");
-    vBool @2 :List(Bool) $Proxy.name("v_bool");
+    vectorBool @2 :List(Bool) $Proxy.name("vector_bool");
     optionalInt @3 :Int32 $Proxy.name("optional_int");
     hasOptionalInt @4 :Bool;
     unorderedSetInt @5 :List(Int32) $Proxy.name("unordered_set_int");
+    mapStringInt @6 :List(StringIntPair) $Proxy.name("map_string_int");
 }
 
 struct FooCustom $Proxy.wrap("mp::test::FooCustom") {
@@ -77,7 +77,7 @@ struct FooMutable {
     message @0 :Text;
 }
 
-struct Pair(T1, T2) {
-    first @0 :T1;
-    second @1 :T2;
+struct StringIntPair {
+    first @0 :Text;
+    second @1 :Int32;
 }
diff --git a/test/mp/test/foo.h b/test/mp/test/foo.h
index 5b66b85e..fc129eab 100644
--- a/test/mp/test/foo.h
+++ b/test/mp/test/foo.h
@@ -22,9 +22,10 @@ struct FooStruct
 {
     std::string name;
     std::set<int> set_int;
-    std::vector<bool> v_bool;
+    std::vector<bool> vector_bool;
     std::optional<int> optional_int;
     std::unordered_set<int> unordered_set_int;
+    std::map<std::string, int> map_string_int;
 };
 
 enum class FooEnum : uint8_t { ONE = 1, TWO = 2, };
@@ -71,7 +72,6 @@ class FooImplementation
     int add(int a, int b) { return a + b; }
     void addOut(int a, int b, int& out) { out = a + b; }
     void addInOut(int x, int& sum) { sum += x; }
-    int mapSize(const std::map<std::string, std::string>& map) { return map.size(); }
     FooStruct pass(FooStruct foo) { return foo; }
     void raise(FooStruct foo) { throw foo; }
     void initThreadMap() {}
diff --git a/test/mp/test/test.cpp b/test/mp/test/test.cpp
index eb4b5ec7..57ee278c 100644
--- a/test/mp/test/test.cpp
+++ b/test/mp/test/test.cpp
@@ -21,6 +21,7 @@
 #include <kj/debug.h>
 #include <kj/memory.h>
 #include <kj/test.h>
+#include <map>
 #include <memory>
 #include <mp/proxy.h>
 #include <mp/proxy.capnp.h>
@@ -146,10 +147,12 @@ KJ_TEST("Call FooInterface methods")
     in.set_int.insert(1);
     in.unordered_set_int.insert(2);
     in.unordered_set_int.insert(1);
-    in.v_bool.push_back(false);
-    in.v_bool.push_back(true);
-    in.v_bool.push_back(false);
+    in.vector_bool.push_back(false);
+    in.vector_bool.push_back(true);
+    in.vector_bool.push_back(false);
     in.optional_int = 3;
+    in.map_string_int.emplace("a", 1);
+    in.map_string_int.emplace("b", 2);
     FooStruct out = foo->pass(in);
     KJ_EXPECT(in.name == out.name);
     KJ_EXPECT(in.set_int.size() == out.set_int.size());
@@ -160,11 +163,16 @@ KJ_TEST("Call FooInterface methods")
     for (const auto& elem : in.unordered_set_int) {
         KJ_EXPECT(out.unordered_set_int.count(elem) == 1);
     }
-    KJ_EXPECT(in.v_bool.size() == out.v_bool.size());
-    for (size_t i = 0; i < in.v_bool.size(); ++i) {
-        KJ_EXPECT(in.v_bool[i] == out.v_bool[i]);
+    KJ_EXPECT(in.vector_bool.size() == out.vector_bool.size());
+    for (size_t i = 0; i < in.vector_bool.size(); ++i) {
+        KJ_EXPECT(in.vector_bool[i] == out.vector_bool[i]);
     }
     KJ_EXPECT(in.optional_int == out.optional_int);
+    KJ_EXPECT(in.map_string_int.size() == out.map_string_int.size());
+    for (auto init{in.map_string_int.begin()}, outit{out.map_string_int.begin()}; init != in.map_string_int.end() && outit != out.map_string_int.end(); ++init, ++outit) {
+        KJ_EXPECT(init->first == outit->first);
+        KJ_EXPECT(init->second == outit->second);
+    }
 
     // Additional checks for std::optional member
     KJ_EXPECT(foo->pass(in).optional_int == 3);