diff --git a/README.md b/README.md
index 80b0fbd354..a4f5fbf47b 100644
--- a/README.md
+++ b/README.md
@@ -78,6 +78,9 @@ object referring to that same position.
of the comment’s start and end are passed as two additional
parameters.
+ Note that you are not allowed to call the parser from the
+ callback—that will corrupt its internal state.
+
- **ranges**: Nodes have their start and end characters offsets
recorded in `start` and `end` properties (directly on the node,
rather than the `loc` object, which holds line/column data. To also
diff --git a/acorn.js b/acorn.js
index ec3d4ed7e2..bbd32cfcea 100644
--- a/acorn.js
+++ b/acorn.js
@@ -77,7 +77,8 @@
// character offsets that denote the start and end of the comment.
// When the `locations` option is on, two more parameters are
// passed, the full `{line, column}` locations of the start and
- // end of the comments.
+ // end of the comments. Note that you are not allowed to call the
+ // parser from the callback—that will corrupt its internal state.
onComment: null,
// Nodes have their start and end characters offsets recorded in
// `start` and `end` properties (directly on the node, rather than
diff --git a/index.html b/index.html
index 9c86b83d78..c1df00bd45 100644
--- a/index.html
+++ b/index.html
@@ -50,7 +50,8 @@ boolean indicating whether this is a block (/* */) comment,
character offsets that denote the start and end of the comment.
When the locations option is on, two more parameters are
passed, the full {line, column} locations of the start and
-end of the comments. | | Nodes have their start and end characters offsets recorded in
+end of the comments. Note that you are not allowed to call the
+parser from the callback—that will corrupt its internal state. | |
| Nodes have their start and end characters offsets recorded in
start and end properties (directly on the node, rather than
the loc object, which holds line/column data. To also add a
semi-standardized range property holding a [start,
|