diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -4514,13 +4514,17 @@
 
     // Adjust the canonical function result type.
     CanQualType CanResultTy = getCanonicalFunctionResultType(ResultTy);
+    const auto OrigCapacity = FunctionProtoTypes.capacity();
     Canonical =
         getFunctionTypeInternal(CanResultTy, CanonicalArgs, CanonicalEPI, true);
 
-    // Get the new insert position for the node we care about.
-    FunctionProtoType *NewIP =
-      FunctionProtoTypes.FindNodeOrInsertPos(ID, InsertPos);
-    assert(!NewIP && "Shouldn't be in the map!"); (void)NewIP;
+    // Get the new insert position for the node we care about, if the recursive
+    // call invalidated InsertPos.
+    if (FunctionProtoTypes.capacity() != OrigCapacity) {
+      FunctionProtoType *NewIP =
+        FunctionProtoTypes.FindNodeOrInsertPos(ID, InsertPos);
+      assert(!NewIP && "Shouldn't be in the map!"); (void)NewIP;
+    }
   }
 
   // Compute the needed size to hold this FunctionProtoType and the