diff --git a/src/ProtoBuf.jl b/src/ProtoBuf.jl
index 9a1f935..b193709 100644
--- a/src/ProtoBuf.jl
+++ b/src/ProtoBuf.jl
@@ -9,10 +9,10 @@ function service_cb(io, t::CodeGenerators.ServiceType, ctx::CodeGenerators.Conte
         response_type = rpc.response_type.name
 
         if rpc.request_type.package_namespace !== nothing
-            request_type = join([rpc.package_namespace, request_type], ".")
+            request_type = join([rpc.request_type.package_namespace, request_type], ".")
         end
         if rpc.response_type.package_namespace !== nothing
-            response_type = join([rpc.package_namespace, response_type], ".")
+            response_type = join([rpc.response_type.package_namespace, response_type], ".")
         end
 
         export_name = "$(service_name)_$(rpc.name)_Client"
diff --git a/test/proto/ext_service.proto b/test/proto/ext_service.proto
new file mode 100644
index 0000000..cb7b7fc
--- /dev/null
+++ b/test/proto/ext_service.proto
@@ -0,0 +1,9 @@
+syntax = "proto3";
+package ext_service;
+
+import "ext_types.proto";
+
+service ExtService {
+  rpc ExtRPC(ext_types.ExtRequest) returns (ext_types.ExtResponse) {}
+  rpc ExtStreamRPC(ext_types.ExtRequest) returns (stream ext_types.ExtResponse) {}
+}
diff --git a/test/proto/ext_types.proto b/test/proto/ext_types.proto
new file mode 100644
index 0000000..91c4bce
--- /dev/null
+++ b/test/proto/ext_types.proto
@@ -0,0 +1,10 @@
+syntax = "proto3";
+package ext_types;
+
+message ExtRequest {
+  uint64 id = 1;
+}
+
+message ExtResponse {
+  uint64 result = 1;
+}
diff --git a/test/runtests.jl b/test/runtests.jl
index 49784eb..29e4a93 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -96,6 +96,25 @@ include("gen/test/test_pb.jl")
             @test contains(generated, "export TestService_TestClientStreamRPC_Client")
             @test contains(generated, "export TestService_TestBidirectionalStreamRPC_Client")
         end
+
+        # Test that request/response type package_namespace is correctly applied when types
+        # come from a different proto package. Previously this was broken because the code
+        # checked rpc.package_namespace instead of rpc.request_type.package_namespace and
+        # rpc.response_type.package_namespace.
+        mktempdir() do tmpdir
+            @test isnothing(protojl("ext_service.proto", joinpath(@__DIR__, "proto"), tmpdir))
+            generated = read(joinpath(tmpdir, "ext_service", "ext_service_pb.jl"), String)
+            # Request type from ext_types package must be prefixed with package namespace
+            @test contains(generated, "ext_types.ExtRequest")
+            # Response type from ext_types package must be prefixed with package namespace
+            @test contains(generated, "ext_types.ExtResponse")
+            # Full type parameter string with both namespaced types
+            @test contains(generated, "gRPCClient.gRPCServiceClient{ext_types.ExtRequest, false, ext_types.ExtResponse, false}")
+            @test contains(generated, "gRPCClient.gRPCServiceClient{ext_types.ExtRequest, false, ext_types.ExtResponse, true}")
+            # Service client constructors are present
+            @test contains(generated, "ExtService_ExtRPC_Client(")
+            @test contains(generated, "ExtService_ExtStreamRPC_Client(")
+        end
     end
 
     @testset "@async varying request/response" begin