diff --git a/iface/CMakeLists.txt b/iface/CMakeLists.txt
index 3b4d9ce..39c2720 100644
--- a/iface/CMakeLists.txt
+++ b/iface/CMakeLists.txt
@@ -9,16 +9,17 @@ target_sources(nf7_iface
   PRIVATE
     version.cc
   PUBLIC
-    observer.hh
+    common/future.hh
+    common/observer.hh
     version.hh
 )
 
 add_executable(nf7_iface_test)
 target_sources(nf7_iface_test
   PRIVATE
-    future_test.cc
-    observer_test.hh
-    observer_test.cc
+    common/future_test.cc
+    common/observer_test.hh
+    common/observer_test.cc
 )
 target_link_libraries(nf7_iface_test
   PRIVATE
diff --git a/iface/exception.hh b/iface/common/exception.hh
similarity index 100%
rename from iface/exception.hh
rename to iface/common/exception.hh
diff --git a/iface/future.hh b/iface/common/future.hh
similarity index 99%
rename from iface/future.hh
rename to iface/common/future.hh
index f840d89..4c04114 100644
--- a/iface/future.hh
+++ b/iface/common/future.hh
@@ -8,7 +8,7 @@
 #include <variant>
 #include <vector>
 
-#include "iface/exception.hh"
+#include "iface/common/exception.hh"
 
 namespace nf7 {
 
diff --git a/iface/future_test.cc b/iface/common/future_test.cc
similarity index 98%
rename from iface/future_test.cc
rename to iface/common/future_test.cc
index c0c8d0e..4432f10 100644
--- a/iface/future_test.cc
+++ b/iface/common/future_test.cc
@@ -1,12 +1,12 @@
 // No copyright
-#include "iface/future.hh"
+#include "iface/common/future.hh"
 
 #include <gtest/gtest.h>
 
 #include <cstdint>
 #include <optional>
 
-#include "iface/exception.hh"
+#include "iface/common/exception.hh"
 
 
 TEST(Future, ImmediateValue) {
diff --git a/iface/observer.hh b/iface/common/observer.hh
similarity index 97%
rename from iface/observer.hh
rename to iface/common/observer.hh
index 553732a..4a1e9fd 100644
--- a/iface/observer.hh
+++ b/iface/common/observer.hh
@@ -7,7 +7,7 @@
 #include <utility>
 
 
-namespace nf7::iface {
+namespace nf7 {
 
 // T is notified to Observer<T> by Observer<T>::Target.
 // All observers should be based on this.
@@ -96,4 +96,4 @@ Observer<T>::~Observer() noexcept {
   target_.Unregister(*this);
 }
 
-}  // namespace nf7::iface
+}  // namespace nf7
diff --git a/iface/observer_test.cc b/iface/common/observer_test.cc
similarity index 77%
rename from iface/observer_test.cc
rename to iface/common/observer_test.cc
index 1ba274b..5bc1283 100644
--- a/iface/observer_test.cc
+++ b/iface/common/observer_test.cc
@@ -1,6 +1,6 @@
 // No copyright
-#include "iface/observer.hh"
-#include "iface/observer_test.hh"
+#include "iface/common/observer.hh"
+#include "iface/common/observer_test.hh"
 
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
@@ -8,12 +8,9 @@
 #include <cstdint>
 #include <optional>
 
-using namespace nf7::iface;
-using namespace nf7::iface::test;
-
 TEST(Observer, NotifyWithMove) {
-  ObserverTargetMock<int32_t> target;
-  ObserverMock<int32_t> sut {target};
+  nf7::test::ObserverTargetMock<int32_t> target;
+  nf7::test::ObserverMock<int32_t> sut {target};
 
   EXPECT_CALL(sut, NotifyWithMove(111)).Times(1);
 
@@ -21,9 +18,9 @@ TEST(Observer, NotifyWithMove) {
 }
 
 TEST(Observer, NotifyWithRef) {
-  ObserverTargetMock<int32_t> target;
-  ObserverMock<int32_t> sut1 {target};
-  ObserverMock<int32_t> sut2 {target};
+  nf7::test::ObserverTargetMock<int32_t> target;
+  nf7::test::ObserverMock<int32_t> sut1 {target};
+  nf7::test::ObserverMock<int32_t> sut2 {target};
 
   EXPECT_CALL(sut1, Notify(111)).Times(1);
   EXPECT_CALL(sut2, Notify(111)).Times(1);
@@ -32,9 +29,9 @@ TEST(Observer, NotifyWithRef) {
 }
 
 TEST(Observer, NotifyDestruction) {
-  std::optional<ObserverTargetMock<int32_t>> target;
+  std::optional<nf7::test::ObserverTargetMock<int32_t>> target;
   target.emplace();
-  ObserverMock<int32_t> sut {*target};
+  nf7::test::ObserverMock<int32_t> sut {*target};
 
   EXPECT_CALL(sut, NotifyDestruction(testing::_)).Times(1);
 
diff --git a/iface/observer_test.hh b/iface/common/observer_test.hh
similarity index 85%
rename from iface/observer_test.hh
rename to iface/common/observer_test.hh
index 6b7ce80..d2b77a6 100644
--- a/iface/observer_test.hh
+++ b/iface/common/observer_test.hh
@@ -1,12 +1,12 @@
 // No copyright
 #pragma once
 
-#include "iface/observer.hh"
+#include "iface/common/observer.hh"
 
 #include <gmock/gmock.h>
 
 
-namespace nf7::iface::test {
+namespace nf7::test {
 
 template <typename T>
 class ObserverMock : public Observer<T> {
@@ -26,4 +26,4 @@ class ObserverTargetMock : public Observer<T>::Target {
   using Observer<T>::Target::Notify;
 };
 
-}  // namespace nf7::iface::test
+}  // namespace nf7::test