diff --git a/src/vim.h b/src/vim.h
index dd04f65..55b9011 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -87,6 +87,13 @@
 # endif
 #endif
 
+// C89 does not define SIZE_MAX
+#if defined(__hpux) || defined(VMS)
+# ifndef SIZE_MAX
+#  define SIZE_MAX ((size_t)(-1))
+# endif
+#endif
+
 // user ID of root is usually zero, but not for everybody
 #ifdef __TANDEM
 # ifndef _TANDEM_SOURCE