diff --git a/crates/wip-protocol/src/validation.rs b/crates/wip-protocol/src/validation.rs
index 7852806..e38eaa8 100644
--- a/crates/wip-protocol/src/validation.rs
+++ b/crates/wip-protocol/src/validation.rs
@@ -315,6 +315,8 @@ pub(crate) fn validate_root_value(
 ) -> Result<(), ValidationError> {
     descriptor.validate()?;
     let declarations = declaration_map(descriptor)?;
+    validate_type_expr(ty, &declarations)
+        .map_err(|error| error.prepend(PathSegment::Interface(descriptor.name.clone())))?;
     validate_value(ty, value, &declarations)
         .map_err(|error| error.prepend(PathSegment::Interface(descriptor.name.clone())))
 }
@@ -369,7 +371,12 @@ fn validate_value(
             _ => expect_kind(value, ValueKind::Json),
         },
         TypeExpr::Named(name) => {
-            validate_declared_value(declarations[name.as_str()], value, declarations)
+            let Some(declaration) = declarations.get(name.as_str()) else {
+                return Err(ValidationError::new(ValidationErrorKind::UnknownType {
+                    name: name.clone(),
+                }));
+            };
+            validate_declared_value(declaration, value, declarations)
         }
     }
 }
diff --git a/crates/wip-protocol/tests/validation.rs b/crates/wip-protocol/tests/validation.rs
index 9495df6..3af79f1 100644
--- a/crates/wip-protocol/tests/validation.rs
+++ b/crates/wip-protocol/tests/validation.rs
@@ -233,6 +233,44 @@ fn named_references_must_exist_and_must_not_cycle() {
         ]
     );
 
+    let valid = descriptor("catalog");
+    let error = valid
+        .validate_value(&TypeExpr::Named("Elsewhere".into()), &Value::Record(vec![]))
+        .unwrap_err();
+    assert_eq!(
+        error.kind,
+        ValidationErrorKind::UnknownType {
+            name: "Elsewhere".into()
+        }
+    );
+    assert_eq!(error.path, vec![PathSegment::Interface("catalog".into())]);
+
+    let error = valid
+        .validate_value(
+            &TypeExpr::Entry {
+                key: Box::new(TypeExpr::String),
+                value: Box::new(TypeExpr::List(Box::new(TypeExpr::Named("Nested".into())))),
+            },
+            &Value::Entry {
+                key: Box::new(Value::String("key".into())),
+                value: Box::new(Value::List(vec![])),
+            },
+        )
+        .unwrap_err();
+    assert_eq!(
+        error.kind,
+        ValidationErrorKind::UnknownType {
+            name: "Nested".into()
+        }
+    );
+    assert_eq!(
+        error.path,
+        vec![
+            PathSegment::Interface("catalog".into()),
+            PathSegment::EntryValue,
+        ]
+    );
+
     let cyclic = InterfaceDescriptor {
         name: "cyclic".into(),
         documentation: None,