diff --git a/src/vim.h b/src/vim.h
index 6fb8978..7d0d128 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -435,6 +435,12 @@
  */
 typedef unsigned int u8char_T;	// int is 32 bits or more
 
+/*
+ * The vimlong_T has sizeof(vimlong_T) >= 2 * sizeof(int).
+ * One use is simple handling of overflow in int calculations.
+ */
+typedef long long vimlong_T;
+
 #ifndef UNIX		    // For Unix this is included in os_unix.h
 # include <stdio.h>
 # include <ctype.h>