diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -71,6 +71,9 @@
 - Fix `#57008 <https://github.com/llvm/llvm-project/issues/57008>`_ - Builtin
   C++ language extension type traits instantiated by a template with unexpected
   number of arguments cause an assertion fault.
+- Fix multi-level pack expansion of undeclared function parameters.
+  This fixes `Issue 56094 <https://github.com/llvm/llvm-project/issues/56094>`_.
+
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -5792,6 +5792,7 @@
                                        = dyn_cast<PackExpansionType>(OldType)) {
       // We have a function parameter pack that may need to be expanded.
       QualType Pattern = Expansion->getPattern();
+      NumExpansions = Expansion->getNumExpansions();
       SmallVector<UnexpandedParameterPack, 2> Unexpanded;
       getSema().collectUnexpandedParameterPacks(Pattern, Unexpanded);
 
diff --git a/clang/test/CXX/temp/temp.decls/temp.variadic/p5.cpp b/clang/test/CXX/temp/temp.decls/temp.variadic/p5.cpp
--- a/clang/test/CXX/temp/temp.decls/temp.variadic/p5.cpp
+++ b/clang/test/CXX/temp/temp.decls/temp.variadic/p5.cpp
@@ -469,3 +469,25 @@
   bar(b);
 }
 }
+
+namespace pr56094 {
+template <typename... T> struct D {
+  template <typename... U> using B = int(int (*...p)(T, U));
+  // expected-error@-1 {{pack expansion contains parameter pack 'U' that has a different length (1 vs. 2) from outer parameter packs}}
+  template <typename U1, typename U2> D(B<U1, U2> *);
+  // expected-note@-1 {{in instantiation of template type alias 'B' requested here}}
+};
+using t1 = D<float>::B<int>;
+// expected-note@-1 {{in instantiation of template class 'pr56094::D<float>' requested here}}
+
+template <bool...> struct F {};
+template <class...> struct G {};
+template <bool... I> struct E {
+  template <bool... U> using B = G<F<I, U>...>;
+  // expected-error@-1 {{pack expansion contains parameter pack 'U' that has a different length (1 vs. 2) from outer parameter packs}}
+  template <bool U1, bool U2> E(B<U1, U2> *);
+  // expected-note@-1 {{in instantiation of template type alias 'B' requested here}}
+};
+using t2 = E<true>::B<false>;
+// expected-note@-1 {{in instantiation of template class 'pr56094::E<true>' requested here}}
+} // namespace pr56094