diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -15879,6 +15879,10 @@
                                     bool CheckParameterNames) {
   bool HasInvalidParm = false;
   for (ParmVarDecl *Param : Parameters) {
+    if (!Param) {
+      HasInvalidParm = true;
+      continue;
+    }
     // C99 6.7.5.3p4: the parameters in a parameter type list in a
     // function declarator that is part of a function definition of
     // that function shall not have incomplete type.
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -1721,6 +1721,8 @@
                                               e = FT->param_type_end();
        i != e; ++i, ++ArgIndex) {
     const ParmVarDecl *PD = FD->getParamDecl(ArgIndex);
+    if (!PD)
+      return false;
     SourceLocation ParamLoc = PD->getLocation();
     if (CheckLiteralType(SemaRef, Kind, ParamLoc, *i,
                          diag::err_constexpr_non_literal_param, ArgIndex + 1,
diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -966,8 +966,11 @@
   if (!Params.empty()) {
     CheckParmsForFunctionDef(Params, /*CheckParameterNames=*/false);
     Method->setParams(Params);
-    for (auto P : Method->parameters())
+    for (auto P : Method->parameters()) {
+      if (!P)
+        continue;
       P->setOwningFunction(Method);
+    }
   }
 
   buildLambdaScopeReturnType(*this, LSI, Method, HasExplicitResultType);
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -1343,7 +1343,7 @@
 
       CXXMethodDecl *MD = Result.getAs<LambdaExpr>()->getCallOperator();
       for (ParmVarDecl *PVD : MD->parameters()) {
-        if (!PVD->hasDefaultArg())
+        if (!PVD || !PVD->hasDefaultArg())
           continue;
         Expr *UninstExpr = PVD->getUninstantiatedDefaultArg();
         // FIXME: Obtain the source location for the '=' token.
diff --git a/clang/test/SemaCXX/crash-params.cpp b/clang/test/SemaCXX/crash-params.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaCXX/crash-params.cpp
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+template <bool>
+int foo() {
+  auto x = [&](__fp16) { return 0; }; // expected-error {{parameters cannot have __fp16 type}}
+  return 0;
+}
+
+int bar() { return foo<true>(); }