diff --git a/clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp b/clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp
--- a/clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp
+++ b/clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp
@@ -144,8 +144,9 @@
     const auto *RightUnaryExpr =
         cast<UnaryExprOrTypeTraitExpr>(Right);
     if (LeftUnaryExpr->isArgumentType() && RightUnaryExpr->isArgumentType())
-      return LeftUnaryExpr->getArgumentType() ==
-             RightUnaryExpr->getArgumentType();
+      return LeftUnaryExpr->getKind() == RightUnaryExpr->getKind() &&
+             LeftUnaryExpr->getArgumentType() ==
+                 RightUnaryExpr->getArgumentType();
     if (!LeftUnaryExpr->isArgumentType() && !RightUnaryExpr->isArgumentType())
       return areEquivalentExpr(LeftUnaryExpr->getArgumentExpr(),
                                RightUnaryExpr->getArgumentExpr());
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -360,6 +360,10 @@
   <clang-tidy/checks/misc/definitions-in-headers>` to avoid warning on
   declarations inside anonymous namespaces.
 
+- Fixed false-positive in :doc:`misc-redundant-expression
+  <clang-tidy/checks/misc/redundant-expression>` check where expressions like
+  ``alignof`` or ``sizeof`` were incorrectly flagged as identical.
+
 - Improved :doc:`misc-unused-parameters
   <clang-tidy/checks/misc/unused-parameters>` check with new `IgnoreVirtual`
   option to optionally ignore virtual methods.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/misc/redundant-expression.cpp b/clang-tools-extra/test/clang-tidy/checkers/misc/redundant-expression.cpp
--- a/clang-tools-extra/test/clang-tidy/checkers/misc/redundant-expression.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/misc/redundant-expression.cpp
@@ -843,3 +843,15 @@
 
   return 2;
 }
+
+namespace PR63096 {
+
+struct alignas(sizeof(int)) X {
+  int x;
+};
+
+static_assert(alignof(X) == sizeof(X));
+static_assert(sizeof(X) == sizeof(X));
+// CHECK-MESSAGES: :[[@LINE-1]]:25: warning: both sides of operator are equivalent
+
+}