diff --git a/docs/languages/r-provider.md b/docs/languages/r-provider.md
index c9065a424..fab46b5b1 100644
--- a/docs/languages/r-provider.md
+++ b/docs/languages/r-provider.md
@@ -123,7 +123,7 @@ Not modelled:
 - **Refused (`unsupported_occurrence`, planning status `unsupported`):**
   - any target that is not a plain `Function` (S4 classes, R6 classes, members);
   - a function whose old or new name is the whole value of a string literal anywhere in the indexed R sources (`UseMethod("area")`, `do.call("f", ...)`, `match.fun`, `get`, `setGeneric`, ...), because string lookup is not resolved. The literal is decoded first, so escapes (`"f\x6fo"`, `"\u{66}oo"`, octal) and raw strings (`r"(foo)"`) count. A string that only contains the name (`"foo(1)"`), a name built at run time (`paste0("fo", "o")`), and strings in files that are not indexed R sources (R Markdown, `NAMESPACE`) are not detected;
-  - a new name `generic.class` whose prefix is an existing function, which would register an S3 method;
+  - a new name `generic.class` where any dot-separated prefix is a function defined in the indexed R sources or a common base generic (`print`, `format`, `summary`, `plot`, `as.character`, ...), which would register an S3 method (`to.json.foo` for a defined `to.json`, `print.foo`);
   - a package function under `R/` that `NAMESPACE` does not mark private (`isExported` is not false), because `NAMESPACE` is not an indexed source and its `export()` or `S3method()` entry would go stale.
 - **Refused by the shared engine (fail-closed, not provider code):** S3 methods and any dotted function name (`area.circle` reads as an owner-qualified member, so `stale_graph`); S4 class names (`unsupported_occurrence`, no exact source-name span); R6 methods (`stale_graph`).
 - **Invalid names (`invalid_name`):** anything that is not a nonreserved R identifier.
diff --git a/gitnexus/src/core/ingestion/languages/r/rename.ts b/gitnexus/src/core/ingestion/languages/r/rename.ts
index 6b2675420..f00272549 100644
--- a/gitnexus/src/core/ingestion/languages/r/rename.ts
+++ b/gitnexus/src/core/ingestion/languages/r/rename.ts
@@ -47,6 +47,40 @@ function rStringValue(text: string): string | null {
     );
 }
 
+/**
+ * Generics of base R and its default packages that an S3 method name `generic.class` can register
+ * against, whether or not the indexed sources define them. Not exhaustive: it covers the generics
+ * a project is most likely to meet by accident, and the repository's own functions are checked
+ * separately.
+ */
+const BASE_GENERICS: ReadonlySet<string> = new Set(
+  (
+    'print format summary plot lines points text image hist barplot boxplot pairs persp ' +
+    'as.character as.data.frame as.list as.vector as.numeric as.integer as.logical as.matrix ' +
+    'as.Date as.POSIXct as.POSIXlt as.factor as.table as.function as.environment as.double ' +
+    'length names dim dimnames levels rev sort unique duplicated anyDuplicated rep seq ' +
+    'mean median quantile range max min round diff scale cut split merge subset transform ' +
+    'with within head tail t c cbind rbind toString all.equal is.na labels str ' +
+    'update predict residuals coef fitted anova simulate terms formula family weights ' +
+    'vcov logLik AIC BIC nobs deviance confint profile model.frame row.names open close ' +
+    'by aggregate droplevels relevel reorder xtfrm solve determinant julian months weekdays'
+  ).split(' '),
+);
+
+/**
+ * Whether `newName` reads as an S3 method `generic.class`: some dot-separated prefix of it is a
+ * function the indexed sources define or a known base generic. Every dot is a possible split
+ * (`to.json.foo` is a method of `to.json`; `as.data.frame.foo` of `as.data.frame`).
+ */
+export function registersS3Method(newName: string, defined: ReadonlySet<string>): boolean {
+  for (let dot = newName.indexOf('.'); dot >= 0; dot = newName.indexOf('.', dot + 1)) {
+    if (dot === 0) continue;
+    const prefix = newName.slice(0, dot);
+    if (defined.has(prefix) || BASE_GENERICS.has(prefix)) return true;
+  }
+  return false;
+}
+
 const unsupported = (message: string): RenameIssue => ({
   code: 'unsupported_occurrence',
   status: 'unsupported',
@@ -114,8 +148,10 @@ export const rRenameProvider: RenameProvider = {
         ),
       ),
     );
-    if (newName.includes('.') && defined.has(newName.slice(0, newName.indexOf('.'))))
-      return unsupported('The new name would register an S3 method of an existing function.');
+    if (registersS3Method(newName, defined))
+      return unsupported(
+        'The new name would register an S3 method of an existing function or base generic.',
+      );
     for (const source of files.values()) {
       if (!source.tree) continue;
       for (const node of walkNamedNodes(source.tree.rootNode)) {
diff --git a/gitnexus/test/fixtures/rename-integration/r/s3-new-method-base-generic/after/helper.R b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-base-generic/after/helper.R
new file mode 100644
index 000000000..94d6da8d4
--- /dev/null
+++ b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-base-generic/after/helper.R
@@ -0,0 +1,5 @@
+helper <- function(v) v + 1
+
+use_helper <- function(v) {
+  helper(v)
+}
diff --git a/gitnexus/test/fixtures/rename-integration/r/s3-new-method-base-generic/before/helper.R b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-base-generic/before/helper.R
new file mode 100644
index 000000000..94d6da8d4
--- /dev/null
+++ b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-base-generic/before/helper.R
@@ -0,0 +1,5 @@
+helper <- function(v) v + 1
+
+use_helper <- function(v) {
+  helper(v)
+}
diff --git a/gitnexus/test/fixtures/rename-integration/r/s3-new-method-base-generic/case.json b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-base-generic/case.json
new file mode 100644
index 000000000..cc76f2783
--- /dev/null
+++ b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-base-generic/case.json
@@ -0,0 +1,9 @@
+{
+  "language": "r",
+  "description": "Refuse a new name that would register a method of a base generic (print.foo), although the repository defines no print().",
+  "categories": ["s3", "name-collision", "negative", "unchanged-on-error"],
+  "target": { "name": "helper", "kind": "Function", "file": "helper.R", "startLine": 0 },
+  "newName": "print.foo",
+  "expect": { "status": "error", "code": "unsupported_occurrence", "planningStatus": "unsupported" },
+  "edges": []
+}
diff --git a/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/after/generics.R b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/after/generics.R
new file mode 100644
index 000000000..2c3fe2be6
--- /dev/null
+++ b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/after/generics.R
@@ -0,0 +1 @@
+to.json <- function(x) UseMethod("to.json")
diff --git a/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/after/helper.R b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/after/helper.R
new file mode 100644
index 000000000..94d6da8d4
--- /dev/null
+++ b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/after/helper.R
@@ -0,0 +1,5 @@
+helper <- function(v) v + 1
+
+use_helper <- function(v) {
+  helper(v)
+}
diff --git a/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/before/generics.R b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/before/generics.R
new file mode 100644
index 000000000..2c3fe2be6
--- /dev/null
+++ b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/before/generics.R
@@ -0,0 +1 @@
+to.json <- function(x) UseMethod("to.json")
diff --git a/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/before/helper.R b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/before/helper.R
new file mode 100644
index 000000000..94d6da8d4
--- /dev/null
+++ b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/before/helper.R
@@ -0,0 +1,5 @@
+helper <- function(v) v + 1
+
+use_helper <- function(v) {
+  helper(v)
+}
diff --git a/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/case.json b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/case.json
new file mode 100644
index 000000000..35d7968ae
--- /dev/null
+++ b/gitnexus/test/fixtures/rename-integration/r/s3-new-method-dotted-generic/case.json
@@ -0,0 +1,9 @@
+{
+  "language": "r",
+  "description": "Refuse a new name whose second dot split names an existing dotted generic (to.json.foo registers a method of to.json).",
+  "categories": ["s3", "name-collision", "negative", "unchanged-on-error"],
+  "target": { "name": "helper", "kind": "Function", "file": "helper.R", "startLine": 0 },
+  "newName": "to.json.foo",
+  "expect": { "status": "error", "code": "unsupported_occurrence", "planningStatus": "unsupported" },
+  "edges": []
+}
diff --git a/gitnexus/test/unit/r-rename-s3-guard.test.ts b/gitnexus/test/unit/r-rename-s3-guard.test.ts
new file mode 100644
index 000000000..0743fe06d
--- /dev/null
+++ b/gitnexus/test/unit/r-rename-s3-guard.test.ts
@@ -0,0 +1,76 @@
+/**
+ * The R rename provider refuses a new name `generic.class` that would silently register an S3
+ * method. Every dot is a possible split, so `to.json.foo` is a method of `to.json`, and a base
+ * generic counts although no indexed source defines it (`print.foo`). Each refusal is paired with
+ * a name that only looks similar.
+ */
+import { describe, expect, it } from 'vitest';
+import Parser from 'tree-sitter';
+import R from '@eagleoutice/tree-sitter-r';
+import { registersS3Method, rRenameProvider } from '../../src/core/ingestion/languages/r/rename.js';
+
+const parser = new Parser();
+parser.setLanguage(R as Parameters<Parser['setLanguage']>[0]);
+
+/** Run the provider's safety check for renaming `helper` to `newName`, with these functions defined. */
+function verdict(newName: string, defined: readonly string[]): string {
+  const source = defined.map((name) => `${name} <- function(x) x`).join('\n');
+  const files = new Map([
+    [
+      'a.R',
+      {
+        tree: parser.parse(source),
+        parsed: { localDefs: defined.map((name) => ({ qualifiedName: name })) },
+      },
+    ],
+  ]);
+  const issue = rRenameProvider.checkSafety?.({
+    target: { type: 'Function', qualifiedName: 'helper', filePath: 'a.R' },
+    newName,
+    files,
+    graph: { forEachNode: () => undefined },
+  } as never);
+  return issue ? issue.code : 'ok';
+}
+
+describe('R rename: the S3 registration guard', () => {
+  it('refuses a name whose first dot split is a defined function', () => {
+    expect(verdict('area.circle', ['area'])).toBe('unsupported_occurrence');
+  });
+
+  it('refuses a name whose later dot split is a defined dotted generic', () => {
+    expect(verdict('to.json.foo', ['to.json'])).toBe('unsupported_occurrence');
+    expect(verdict('as.data.frame.foo', ['as.data.frame'])).toBe('unsupported_occurrence');
+  });
+
+  it('refuses a name with one dot after a defined function of a shorter name', () => {
+    expect(verdict('to.json', ['to'])).toBe('unsupported_occurrence');
+  });
+
+  it('refuses a method of a base generic that the sources do not define', () => {
+    for (const name of ['print.foo', 'format.foo', 'summary.foo', 'plot.foo', 'as.character.foo']) {
+      expect(verdict(name, [])).toBe('unsupported_occurrence');
+    }
+  });
+
+  it('allows a dotted name when no prefix is a function or a base generic', () => {
+    expect(verdict('my.helper', [])).toBe('ok');
+    expect(verdict('to.json.foo', [])).toBe('ok');
+    expect(verdict('toJson.foo', ['to.json'])).toBe('ok');
+  });
+
+  it('allows a name with no dot, and a name that merely starts with a dot', () => {
+    expect(verdict('print_foo', [])).toBe('ok');
+    expect(verdict('.print', [])).toBe('ok');
+    expect(verdict('.print.x', [])).toBe('ok');
+  });
+
+  it('tests every prefix of the name', () => {
+    const defined = new Set(['a.b']);
+    expect([
+      registersS3Method('a.b.c.d', defined),
+      registersS3Method('a.x.b', defined),
+      registersS3Method('a.b', defined),
+    ]).toEqual([true, false, false]);
+  });
+});