diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -2472,7 +2472,7 @@
         const auto *PrevPrev = Prev ? Prev->getPreviousNonComment() : nullptr;
         const bool Blacklisted =
             PrevPrev &&
-            (PrevPrev->is(tok::kw___attribute) ||
+            (PrevPrev->isOneOf(tok::kw___attribute, tok::kw_decltype) ||
              (SeenEqual &&
               (PrevPrev->isOneOf(tok::kw_if, tok::kw_while) ||
                PrevPrev->endsSequence(tok::kw_constexpr, tok::kw_if))));
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -26313,6 +26313,7 @@
 
   Style.RemoveParentheses = FormatStyle::RPS_MultipleParentheses;
   verifyFormat("int x __attribute__((aligned(16))) = 0;", Style);
+  verifyFormat("decltype((foo->bar)) baz;", Style);
   verifyFormat("class __declspec(dllimport) X {};",
                "class __declspec((dllimport)) X {};", Style);
   verifyFormat("int x = (({ 0; }));", "int x = ((({ 0; })));", Style);