diff --git a/clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp b/clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp
index 149d63ff1e62fa..669132024af773 100644
--- a/clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp
@@ -135,6 +135,9 @@ void UnusedParametersCheck::warnOnUnusedParameter(
     const MatchFinder::MatchResult &Result, const FunctionDecl *Function,
     unsigned ParamIndex) {
   const auto *Param = Function->getParamDecl(ParamIndex);
+  // Don't bother to diagnose invalid parameters as being unused.
+  if (Param->isInvalidDecl())
+    return;
   auto MyDiag = diag(Param->getLocation(), "parameter %0 is unused") << Param;
 
   if (!Indexer) {
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 1f1c4c87112aa2..7a660c0230cbe4 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -110,6 +110,9 @@ Improvements to clang-tidy
   from suppressing diagnostics associated with macro arguments. This fixes
   `Issue 55134 <https://github.com/llvm/llvm-project/issues/55134>`_.
 
+- Invalid parameters are no longer treated as being implicitly unused for the
+  `-misc-unused-parameters` check. This fixes `Issue 56152 <https://github.com/llvm/llvm-project/issues/56152>`_.
+
 New checks
 ^^^^^^^^^^
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/misc-unused-invalid-parameter.cpp b/clang-tools-extra/test/clang-tidy/checkers/misc-unused-invalid-parameter.cpp
new file mode 100644
index 00000000000000..e7642e79b1a474
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/misc-unused-invalid-parameter.cpp
@@ -0,0 +1,10 @@
+// RUN: %check_clang_tidy -fix-errors %s misc-unused-parameters %t
+
+namespace GH56152 {
+// There's no way to know whether the parameter is used or not if the parameter
+// is an invalid declaration. Ensure the diagnostic is suppressed in this case.
+void func(unknown_type value) { // CHECK-MESSAGES: :[[@LINE]]:11: error: unknown type name 'unknown_type'
+  value += 1;
+}
+}
+