diff --git a/src/vim.h b/src/vim.h
index 251e190..99afe29 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -312,11 +312,12 @@
 #define NUMBUFLEN 65
 
 // flags for vim_str2nr()
-#define STR2NR_BIN 0x01
-#define STR2NR_OCT 0x02
-#define STR2NR_HEX 0x04
-#define STR2NR_ALL (STR2NR_BIN + STR2NR_OCT + STR2NR_HEX)
-#define STR2NR_NO_OCT (STR2NR_BIN + STR2NR_HEX)
+#define STR2NR_BIN  0x01
+#define STR2NR_OCT  0x02
+#define STR2NR_HEX  0x04
+#define STR2NR_OOCT 0x08    // Octal with prefix "0o": 0o777
+#define STR2NR_ALL (STR2NR_BIN + STR2NR_OCT + STR2NR_HEX + STR2NR_OOCT)
+#define STR2NR_NO_OCT (STR2NR_BIN + STR2NR_HEX + STR2NR_OOCT)
 
 #define STR2NR_FORCE 0x80   // only when ONE of the above is used