diff --git a/CHANGELOG.md b/CHANGELOG.md
index cf5e47d..6b03520 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,8 @@ Second pre-release. Continues the W3C XSTS schema-validity campaign: **invalid-s
 
 ### Fixed
 
+- XSTS invalid-schemas-accepted (#145): a referencing `attributeGroup` (one carrying a `ref`) is held to its `(annotation?)` content model. It names a definition elsewhere, so it may not itself declare attributes, nested attributeGroup references, or an `anyAttribute`; only a defining `attributeGroup` (with `name`) carries those (`attgD`). Caught three invalid schemas: invalid-schemas-accepted 210 → 207, no other bucket moved.
+
 - XSTS invalid-schemas-accepted (#145): notation names are now part of the component-name uniqueness check. A notation has its own symbol space, so two notations sharing a name and target namespace are a duplicate just as two global types or elements would be (`notatB005`). Caught one invalid schema: invalid-schemas-accepted 211 → 210, no other bucket moved.
 
 - XSTS invalid-schemas-accepted (#145): an `xsd:notation` declaration is held to its `(annotation?)` content model. A notation may carry only an optional `annotation` child, so any other element child, or any non-whitespace character content, is now rejected (`notatG`). Caught three invalid schemas: invalid-schemas-accepted 214 → 211, no other bucket moved.
diff --git a/Sources/Schema/SchemaStructureHelpers.swift b/Sources/Schema/SchemaStructureHelpers.swift
index 1a394bc..d1e32c1 100644
--- a/Sources/Schema/SchemaStructureHelpers.swift
+++ b/Sources/Schema/SchemaStructureHelpers.swift
@@ -169,7 +169,16 @@ extension PureXML.Schema.XSDParser {
         return errors
     }
 
-    static func attributeGroupChildrenErrors(_: XSDTree, names: [String]) -> [String] {
+    static func attributeGroupChildrenErrors(_ node: XSDTree, names: [String]) -> [String] {
+        // A referencing attributeGroup (one with `ref`) names a definition elsewhere;
+        // its own content model is (annotation?), so it may not also declare
+        // attributes, nested attributeGroup references, or an anyAttribute. Only a
+        // defining attributeGroup (with `name`) carries those.
+        if PureXML.Schema.XSDNode.attribute(node, "ref") != nil {
+            return names.contains { $0 != "annotation" }
+                ? ["an attributeGroup reference may contain only an optional annotation"]
+                : []
+        }
         var errors: [String] = []
         let anyAttributes = names.count { $0 == "anyAttribute" }
         if anyAttributes > 1 {
diff --git a/Tests/XSTSSuiteTests.swift b/Tests/XSTSSuiteTests.swift
index acfde00..a52dc2d 100644
--- a/Tests/XSTSSuiteTests.swift
+++ b/Tests/XSTSSuiteTests.swift
@@ -113,8 +113,12 @@ struct XSTSSuiteTests {
     /// symbol space; two notations of the same name and namespace clash) then caught
     /// one more invalid schema: invalid-schemas accepted 211 → 210, no other bucket
     /// moved.
+    /// Holding a referencing `attributeGroup` (one with `ref`) to its `(annotation?)`
+    /// content model, so it may not also declare attributes, nested attributeGroup
+    /// references, or an anyAttribute, then caught three more invalid schemas:
+    /// invalid-schemas accepted 210 → 207, no other bucket moved.
     private let knownSchemaValidRejected = 1
-    private let knownSchemaInvalidAccepted = 210
+    private let knownSchemaInvalidAccepted = 207
     private let knownInstanceValidRejected = 3
     private let knownInstanceInvalidAccepted = 132