diff --git a/gas.md b/gas.md
index fa70224ec..9a0287902 100644
--- a/gas.md
+++ b/gas.md
@@ -422,7 +422,10 @@ NOTE: (continuation) The above may be too complex, so then we may want to have
     sum [registerLoadDelta(r, v) | (r, v) <- getReturns() `zip` rVALUES]
   ```
 
-#### `STOP` and `REVERT`
+#### `INVALID`, `STOP`, `REVERT` and exceptions
+
+`INVALID` generates an exception, but many other things do, including being
+out of gas, which means that there may not be any gas to pay for the exception.
 
 * `STOP`
   ```hs