diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -301,6 +301,8 @@
   expressions/statements with invalid source locations in non-assert builds. 
   Assert builds may still see assertions triggered from this.
   (`#62105 <https://github.com/llvm/llvm-project/issues/62105>`_)
+- Fix crash when handling undefined template partial specialization
+  (`#61356 <https://github.com/llvm/llvm-project/issues/61356>`_)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaCXXScopeSpec.cpp b/clang/lib/Sema/SemaCXXScopeSpec.cpp
--- a/clang/lib/Sema/SemaCXXScopeSpec.cpp
+++ b/clang/lib/Sema/SemaCXXScopeSpec.cpp
@@ -125,7 +125,7 @@
             PartialSpec = ClassTemplate->findPartialSpecialization(ContextType);
           }
 
-          if (PartialSpec) {
+          if (PartialSpec && PartialSpec->hasDefinition()) {
             // A declaration of the partial specialization must be visible.
             // We can always recover here, because this only happens when we're
             // entering the context, and that can't happen in a SFINAE context.
diff --git a/clang/test/SemaCXX/undefined-partial-specialization.cpp b/clang/test/SemaCXX/undefined-partial-specialization.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaCXX/undefined-partial-specialization.cpp
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -std=c++20 -verify %s
+
+namespace GH61356 {
+
+template <typename T, bool b>
+class boo {void foo();};
+
+template <typename T>
+class boo<T, true>;
+
+template<typename T>
+void boo<T, true>::foo(){} // expected-error{{nested name specifier 'boo<T, true>::' for declaration does not refer into a class, class template or class template partial specialization}}
+
+}