diff --git a/R/S4.R b/R/S4.R
index 88937ba9..f01179ba 100644
--- a/R/S4.R
+++ b/R/S4.R
@@ -45,13 +45,13 @@ S4_to_S7_class <- function(x, error_base = "", call = sys.call(-1L)) {
   # Convert generator function to class
   if (methods::is(x, "classGeneratorFunction")) {
     return(S4_to_S7_class(
-      methods::getClass(as.character(x@className)),
+      methods::getClass(x@className),
       error_base,
       call = call
     ))
   }
 
-  if (methods::is(x, "ClassUnionRepresentation")) {
+  if (methods::isClassUnion(x)) {
     subclasses <- Filter(function(y) y@distance == 1, x@subclasses)
     subclasses <- lapply(subclasses, function(x) methods::getClass(x@subClass))
     do.call("new_union", subclasses)
@@ -62,8 +62,8 @@ S4_to_S7_class <- function(x, error_base = "", call = sys.call(-1L)) {
         return(basic_classes[[x@className]])
       }
     }
-    if (methods::extends(x, "oldClass")) {
-      new_S3_class(as.character(x@className))
+    if (is_oldClass(x)) {
+      new_S3_class(methods::extends(x))
     } else {
       x
     }
@@ -129,7 +129,8 @@ S4_class_dispatch <- function(x) {
 }
 
 is_oldClass <- function(x) {
-  x@virtual && methods::extends(x, "oldClass") && x@className != "oldClass"
+  methods::extends(x, "oldClass") &&
+    x@className %in% attr(x@prototype, ".S3Class")
 }
 
 S4_class_name <- function(x) {
diff --git a/tests/testthat/test-S4.R b/tests/testthat/test-S4.R
index 7b01a6a0..56c37210 100644
--- a/tests/testthat/test-S4.R
+++ b/tests/testthat/test-S4.R
@@ -124,6 +124,21 @@ describe("S4_class_dispatch", {
     )
   })
 
+  it("dispatches through the full S3 old-class hierarchy", {
+    on.exit(S4_remove_classes(c("S4OldS3Child", "S4OldS3a", "S4OldS3b")))
+
+    setOldClass(c("S4OldS3a", "S4OldS3b"))
+    setClass("S4OldS3Child", contains = "S4OldS3a")
+
+    generic <- new_generic("S4OldS3Generic", "x")
+    method(generic, new_S3_class("S4OldS3b")) <- function(x) "S3 parent"
+
+    object <- methods::new("S4OldS3Child")
+
+    expect_contains(obj_dispatch(object), "S4OldS3b")
+    expect_equal(generic(object), "S3 parent")
+  })
+
   it("ignores unions", {
     on.exit(S4_remove_classes(c("Foo1", "Foo2", "Foo3")))