diff --git a/CMakeLists.txt b/CMakeLists.txt
index a92878781b..0b9ad284ab 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -731,8 +731,8 @@ set(HOST_TARGET_TRIPLE "${HOST_TARGET_ARCH}-${HOST_TARGET_OS}")
 
 if(MSVC)
   set(ZIG_WASM2C_COMPILE_FLAGS "")
-  set(ZIG1_COMPILE_FLAGS "/std:c99 /Os")
-  set(ZIG2_COMPILE_FLAGS "/std:c99 /O0")
+  set(ZIG1_COMPILE_FLAGS "/Os")
+  set(ZIG2_COMPILE_FLAGS "/O0")
   set(ZIG2_LINK_FLAGS "/STACK:16777216")
 else()
   set(ZIG_WASM2C_COMPILE_FLAGS "-std=c99 -O2")