diff --git a/cmake/CheckFunctionExistsEx.c b/cmake/CheckFunctionExistsEx.c
index 5ee3e591..224e3404 100644
--- a/cmake/CheckFunctionExistsEx.c
+++ b/cmake/CheckFunctionExistsEx.c
@@ -1,30 +1,28 @@
 #ifdef CHECK_FUNCTION_EXISTS
 
-#ifndef _WIN32
-char CHECK_FUNCTION_EXISTS();
+#ifdef __cplusplus
+extern "C"
 #endif
-
+  char
+  CHECK_FUNCTION_EXISTS(void);
 #ifdef __CLASSIC_C__
-int main(){
+int main()
+{
   int ac;
-  char*av[];
+  char* av[];
 #else
-int main(int ac, char*av[]){
+int main(int ac, char* av[])
+{
 #endif
-#ifdef _WIN32
-  void * p = &CHECK_FUNCTION_EXISTS;
-#else
   CHECK_FUNCTION_EXISTS();
-#endif
-  if(ac > 1000)
-    {
+  if (ac > 1000) {
     return *av[0];
-    }
+  }
   return 0;
 }
 
-#else  /* CHECK_FUNCTION_EXISTS */
+#else /* CHECK_FUNCTION_EXISTS */
 
-#  error "CHECK_FUNCTION_EXISTS has to specify the function"
+#error "CHECK_FUNCTION_EXISTS has to specify the function"
 
 #endif /* CHECK_FUNCTION_EXISTS */