diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index aa91539..c55b34d 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -4738,7 +4738,7 @@
 	    while ((pos = (char_u *)strstr((char *)pos + 2, "$*")) != NULL)
 		++i;
 	    len = (int)STRLEN(p);
-	    new_cmdline = alloc(STRLEN(program) + i * (len - 2) + 1);
+	    new_cmdline = alloc(STRLEN(program) + (size_t)i * (len - 2) + 1);
 	    if (new_cmdline == NULL)
 		return NULL;			// out of memory
 	    ptr = new_cmdline;