diff --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/clang/lib/Parse/ParseExprCXX.cpp
@@ -1862,9 +1862,11 @@
     CommaLocsTy CommaLocs;
 
     auto RunSignatureHelp = [&]() {
-      QualType PreferredType = Actions.ProduceConstructorSignatureHelp(
-          getCurScope(), TypeRep.get()->getCanonicalTypeInternal(),
-          DS.getEndLoc(), Exprs, T.getOpenLocation());
+      QualType PreferredType;
+      if (TypeRep)
+        PreferredType = Actions.ProduceConstructorSignatureHelp(
+            getCurScope(), TypeRep.get()->getCanonicalTypeInternal(),
+            DS.getEndLoc(), Exprs, T.getOpenLocation());
       CalledSignatureHelp = true;
       return PreferredType;
     };
@@ -3038,9 +3040,10 @@
       auto RunSignatureHelp = [&]() {
         ParsedType TypeRep =
             Actions.ActOnTypeName(getCurScope(), DeclaratorInfo).get();
+        assert(TypeRep && "invalid types should be handled by that point");
         QualType PreferredType = Actions.ProduceConstructorSignatureHelp(
-            getCurScope(), TypeRep.get()->getCanonicalTypeInternal(),
-            DeclaratorInfo.getEndLoc(), ConstructorArgs, ConstructorLParen);
+              getCurScope(), TypeRep.get()->getCanonicalTypeInternal(),
+              DeclaratorInfo.getEndLoc(), ConstructorArgs, ConstructorLParen);
         CalledSignatureHelp = true;
         return PreferredType;
       };
diff --git a/clang/unittests/Sema/CodeCompleteTest.cpp b/clang/unittests/Sema/CodeCompleteTest.cpp
--- a/clang/unittests/Sema/CodeCompleteTest.cpp
+++ b/clang/unittests/Sema/CodeCompleteTest.cpp
@@ -481,4 +481,12 @@
   )cpp";
   EXPECT_THAT(collectPreferredTypes(Code), Each("vector<int>"));
 }
+
+TEST(PreferredTypeTest, NoCrashOnInvalidFunctionCasts) {
+  StringRef Code = R"cpp(
+    auto x = decltype(&1)(^);
+    auto y = new decltype(&1)(^);
+  )cpp";
+  EXPECT_THAT(collectPreferredTypes(Code), Each("NULL TYPE"));
+}
 } // namespace