diff --git a/CMakeLists.txt b/CMakeLists.txt
index 711af552..0082c448 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -137,7 +137,7 @@ endif()
 if(MI_DEBUG_TSAN MATCHES "ON") 
   if(CMAKE_C_COMPILER_ID MATCHES "Clang")
     message(STATUS "Build with thread sanitizer (MI_DEBUG_TSAN=ON)")
-    list(APPEND mi_cflags -fsanitize=thread -g)
+    list(APPEND mi_cflags -fsanitize=thread -g -O1)
     list(APPEND CMAKE_EXE_LINKER_FLAGS -fsanitize=thread)
   else()
     message(WARNING "Can only use thread sanitizer with clang (MI_DEBUG_TSAN=ON but ignored)")