diff --git a/lib/Sema/SemaTemplateInstantiateDecl.cpp b/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 48b517e..8974ecb 100644
--- a/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -1776,28 +1776,32 @@
   if (NewTInfo != OldTInfo) {
     // Get parameters from the new type info.
     TypeLoc OldTL = OldTInfo->getTypeLoc();
-    FunctionProtoTypeLoc *OldProtoLoc = cast<FunctionProtoTypeLoc>(&OldTL);
-    TypeLoc NewTL = NewTInfo->getTypeLoc();
-    FunctionProtoTypeLoc *NewProtoLoc = cast<FunctionProtoTypeLoc>(&NewTL);
-    assert(NewProtoLoc && "Missing prototype?");
-    for (unsigned i = 0, i_end = NewProtoLoc->getNumArgs(); i != i_end; ++i) {
-      // FIXME: Variadic templates will break this.
-      Params.push_back(NewProtoLoc->getArg(i));
-      SemaRef.CurrentInstantiationScope->InstantiatedLocal(
+    if (FunctionProtoTypeLoc *OldProtoLoc
+                                  = dyn_cast<FunctionProtoTypeLoc>(&OldTL)) {
+      TypeLoc NewTL = NewTInfo->getTypeLoc();
+      FunctionProtoTypeLoc *NewProtoLoc = cast<FunctionProtoTypeLoc>(&NewTL);
+      assert(NewProtoLoc && "Missing prototype?");
+      for (unsigned i = 0, i_end = NewProtoLoc->getNumArgs(); i != i_end; ++i) {
+        // FIXME: Variadic templates will break this.
+        Params.push_back(NewProtoLoc->getArg(i));
+        SemaRef.CurrentInstantiationScope->InstantiatedLocal(
                                                         OldProtoLoc->getArg(i),
                                                         NewProtoLoc->getArg(i));
+      }
     }
   } else {
     // The function type itself was not dependent and therefore no
     // substitution occurred. However, we still need to instantiate
     // the function parameters themselves.
     TypeLoc OldTL = OldTInfo->getTypeLoc();
-    FunctionProtoTypeLoc *OldProtoLoc = cast<FunctionProtoTypeLoc>(&OldTL);
-    for (unsigned i = 0, i_end = OldProtoLoc->getNumArgs(); i != i_end; ++i) {
-      ParmVarDecl *Parm = VisitParmVarDecl(OldProtoLoc->getArg(i));
-      if (!Parm)
-        return 0;
-      Params.push_back(Parm);
+    if (FunctionProtoTypeLoc *OldProtoLoc
+                                    = dyn_cast<FunctionProtoTypeLoc>(&OldTL)) {
+      for (unsigned i = 0, i_end = OldProtoLoc->getNumArgs(); i != i_end; ++i) {
+        ParmVarDecl *Parm = VisitParmVarDecl(OldProtoLoc->getArg(i));
+        if (!Parm)
+          return 0;
+        Params.push_back(Parm);
+      }
     }
   }
   return NewTInfo;