diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1f368571..886bc873 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -80,7 +80,7 @@ set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
 # libsora.a を作る
 
 add_library(sora STATIC)
-set_target_properties(sora PROPERTIES CXX_STANDARD 20 C_STANDARD 20)
+set_target_properties(sora PROPERTIES CXX_STANDARD 17 C_STANDARD 17)
 
 string(SUBSTRING "${SORA_CPP_SDK_COMMIT}" 0 8 SORA_CPP_SDK_COMMIT_SHORT)
 string(SUBSTRING "${WEBRTC_COMMIT}" 0 8 WEBRTC_COMMIT_SHORT)
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 28ca482e..8b38acba 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -33,7 +33,7 @@ if (USE_LYRA)
 endif()
 
 function (init_target target)
-  set_target_properties(${target} PROPERTIES CXX_STANDARD 20 C_STANDARD 20)
+  set_target_properties(${target} PROPERTIES CXX_STANDARD 17 C_STANDARD 17)
   set_target_properties(${target} PROPERTIES POSITION_INDEPENDENT_CODE ON)
   target_link_libraries(${target} PRIVATE Sora::sora)