diff --git a/engine/CMakeLists.txt b/engine/CMakeLists.txt
index 58fe544d..5a1425fc 100644
--- a/engine/CMakeLists.txt
+++ b/engine/CMakeLists.txt
@@ -157,6 +157,9 @@ if(BUILD_TESTING)
     add_test(NAME segmentation_contract COMMAND test_segmentation_contract)
 
     add_executable(test_windows_ipc_contract contracts/tests/windows_ipc_contract.cpp)
+    if(MSVC)
+        target_compile_options(test_windows_ipc_contract PRIVATE /utf-8)
+    endif()
     add_test(NAME windows_ipc_contract COMMAND test_windows_ipc_contract)
 
     add_executable(test_punctuation_contract contracts/tests/punctuation_contract.cpp)
diff --git a/server/tests/portable/CMakeLists.txt b/server/tests/portable/CMakeLists.txt
index 7d8c6692..542057af 100644
--- a/server/tests/portable/CMakeLists.txt
+++ b/server/tests/portable/CMakeLists.txt
@@ -32,7 +32,10 @@ if(MSIME_PORTABLE_TESTS_SANITIZE AND NOT MSVC)
     target_link_options(portable_tests PRIVATE -fsanitize=address,undefined)
 endif()
 
-if(NOT MSVC)
+if(MSVC)
+    # Standalone project, so the server's directory-wide /utf-8 does not reach it.
+    target_compile_options(portable_tests PRIVATE /utf-8)
+else()
     target_compile_options(portable_tests PRIVATE -Wall -Wextra -Wpedantic -Werror)
 endif()
 
diff --git a/tests/pipe-probe/CMakeLists.txt b/tests/pipe-probe/CMakeLists.txt
index 9ac39505..b89c5c47 100644
--- a/tests/pipe-probe/CMakeLists.txt
+++ b/tests/pipe-probe/CMakeLists.txt
@@ -8,3 +8,6 @@ add_executable(msime-ipc-probe main.cpp)
 target_compile_features(msime-ipc-probe PRIVATE cxx_std_17)
 target_compile_definitions(msime-ipc-probe PRIVATE NOMINMAX UNICODE _UNICODE)
 target_include_directories(msime-ipc-probe PRIVATE "${MSIME_CONTRACTS_DIR}")
+if(MSVC)
+    target_compile_options(msime-ipc-probe PRIVATE /utf-8)
+endif()
diff --git a/ui/CMakeLists.txt b/ui/CMakeLists.txt
index ebaab879..ce64f633 100644
--- a/ui/CMakeLists.txt
+++ b/ui/CMakeLists.txt
@@ -143,6 +143,9 @@ target_link_libraries(msimeui-handwriting-demo PRIVATE msimeui windowsapp.lib)
 target_compile_features(msimeui-handwriting-demo PRIVATE cxx_std_20)
 
 if(MSVC)
+    # include/msimeui/Controls.h is UTF-8 without a BOM, so every consumer of msimeui has to read
+    # it as UTF-8 too; otherwise a CJK-locale build (code page 936) swallows lines and fails.
+    target_compile_options(msimeui PUBLIC /utf-8)
     target_compile_options(msimeui PRIVATE /W4 /permissive-)
     target_compile_options(msimeui-demo PRIVATE /W4 /permissive-)
     target_compile_options(msimeui-emoji-panel PRIVATE /W4 /permissive-)
diff --git a/windows/CMakeLists.txt b/windows/CMakeLists.txt
index 4e3e3b07..04ea68b8 100644
--- a/windows/CMakeLists.txt
+++ b/windows/CMakeLists.txt
@@ -13,6 +13,9 @@ project(${PROJECT_NAME} LANGUAGES CXX C)
 # Release binaries need usable symbols for crash diagnosis. Keep the PDB beside the DLL so the
 # release job can validate and publish it without changing the binary's install layout.
 if(MSVC)
+    # Sources are UTF-8 without a BOM and hold wide punctuation literals (L"“" and the like). /utf-8
+    # used to arrive only through fmt's interface options, which the tests below never link.
+    add_compile_options(/utf-8)
     set(CMAKE_MSVC_DEBUG_INFORMATION_FORMAT "ProgramDatabase")
     add_compile_options("$<$<CONFIG:Release>:/Zi>")
     add_link_options("$<$<CONFIG:Release>:/DEBUG>")
diff --git a/windows/tests/CMakeLists.txt b/windows/tests/CMakeLists.txt
index 6a44dc6f..e3e2b506 100644
--- a/windows/tests/CMakeLists.txt
+++ b/windows/tests/CMakeLists.txt
@@ -4,6 +4,10 @@ cmake_minimum_required(VERSION 3.25)
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
     project(MsimeTsfLocalPolicyTests LANGUAGES CXX)
     enable_testing()
+    # windows/CMakeLists.txt sets this for the in-tree build; the sources and headers are UTF-8.
+    if(MSVC)
+        add_compile_options(/utf-8)
+    endif()
 endif()
 
 add_executable(test_client_fallback client_fallback.cpp)