diff --git a/src/c/main.d b/src/c/main.d
index 981da13c0..1d0ecb0a4 100755
--- a/src/c/main.d
+++ b/src/c/main.d
@@ -201,7 +201,7 @@ _ecl_dealloc_env(cl_env_ptr env)
     ecl_internal_error("Unable to deallocate environment structure.");
 #else
 # if defined(ECL_USE_GUARD_PAGE)
-  if (!VirtualFree(env, sizeof(*env), MEM_RELEASE))
+  if (!VirtualFree(env, 0, MEM_RELEASE))
     ecl_internal_error("Unable to deallocate environment structure.");
 # endif
 #endif