diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index a6b432f..003615e 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -59,6 +59,10 @@ elseif(UNIX)
   set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,--build-id")
 endif()
 
+if (MSVC)
+  add_compile_options(/wd4146 /wd4703 -D_CRT_SECURE_NO_WARNINGS)
+endif()
+
 enable_testing()
 
 add_library(port INTERFACE)
diff --git a/upb/json_decode.c b/upb/json_decode.c
index bb33744..1fadd26 100644
--- a/upb/json_decode.c
+++ b/upb/json_decode.c
@@ -1160,7 +1160,7 @@ static void jsondec_struct(jsondec *d, upb_msg *msg, const upb_msgdef *m) {
 static void jsondec_wellknownvalue(jsondec *d, upb_msg *msg,
                                    const upb_msgdef *m) {
   upb_msgval val;
-  const upb_fielddef *f;
+  const upb_fielddef *f = NULL;
   upb_msg *submsg;
 
   switch (jsondec_peek(d)) {