diff --git a/cmake/ci.cmake b/cmake/ci.cmake
index 01cd7c75d..c34f8603f 100644
--- a/cmake/ci.cmake
+++ b/cmake/ci.cmake
@@ -408,7 +408,7 @@ endforeach()
 # Sanitizers.
 ###############################################################################
 
-set(CLANG_CXX_FLAGS_SANITIZER "-g -O0 -fsanitize=address -fsanitize=undefined -fsanitize=integer -fsanitize=nullability -fno-omit-frame-pointer -fno-sanitize-recover=all -fsanitize-recover=unsigned-integer-overflow")
+set(CLANG_CXX_FLAGS_SANITIZER "-g -O1 -fsanitize=address -fsanitize=undefined -fsanitize=integer -fsanitize=nullability -fno-omit-frame-pointer -fno-sanitize-recover=all -fsanitize-recover=unsigned-integer-overflow")
 
 add_custom_target(ci_test_clang_sanitizer
     COMMAND CXX=${CLANG_TOOL} CXXFLAGS=${CLANG_CXX_FLAGS_SANITIZER} ${CMAKE_COMMAND}