diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 375c75c..0bca475 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -222,7 +222,7 @@
     Res.push_back("-verify");
   if (Opts.ShowOptionNames)
     Res.push_back("-fdiagnostics-show-option");
-  if (Opts.TabStop != 8) {
+  if (Opts.TabStop != DiagnosticOptions::DefaultTabStop) {
     Res.push_back("-ftabstop");
     Res.push_back(llvm::utostr(Opts.TabStop));
   }
@@ -808,7 +808,13 @@
   Opts.ShowOptionNames = Args.hasArg(OPT_fdiagnostics_show_option);
   Opts.ShowSourceRanges = Args.hasArg(OPT_fdiagnostics_print_source_range_info);
   Opts.VerifyDiagnostics = Args.hasArg(OPT_verify);
-  Opts.TabStop = getLastArgIntValue(Args, OPT_ftabstop, 8, Diags);
+  Opts.TabStop = getLastArgIntValue(Args, OPT_ftabstop,
+                                    DiagnosticOptions::DefaultTabStop, Diags);
+  if (Opts.TabStop == 0 || Opts.TabStop > DiagnosticOptions::MaxTabStop) {
+    Diags.Report(diag::warn_ignoring_ftabstop_value)
+      << Opts.TabStop << DiagnosticOptions::DefaultTabStop;
+    Opts.TabStop = DiagnosticOptions::DefaultTabStop;
+  }
   Opts.MessageLength = getLastArgIntValue(Args, OPT_fmessage_length, 0, Diags);
   Opts.DumpBuildInformation = getLastArgValue(Args, OPT_dump_build_information);
   Opts.Warnings = getAllArgValues(Args, OPT_W);