3 files changed, 7 insertions, 2 deletions
diff --git a/printing/print_job_constants.h b/printing/print_job_constants.h
index 99b2892..ebd63c2 100644
--- a/printing/print_job_constants.h
+++ b/printing/print_job_constants.h
@@ -49,6 +49,7 @@ PRINTING_EXPORT extern const int COMPLETE_PREVIEW_DOCUMENT_INDEX;
 
 // Print job duplex mode values.
 enum DuplexMode {
+  UNKNOWN_DUPLEX_MODE = -1,
   SIMPLEX,
   LONG_EDGE,
   SHORT_EDGE,
diff --git a/printing/printing_context_mac.mm b/printing/printing_context_mac.mm
index 8ba4db8..3534496 100644
--- a/printing/printing_context_mac.mm
+++ b/printing/printing_context_mac.mm
@@ -236,9 +236,11 @@ bool PrintingContextMac::SetDuplexModeInPrintSettings(DuplexMode mode) {
     case SHORT_EDGE:
       duplexSetting = kPMDuplexTumble;
       break;
-    default:
+    case SIMPLEX:
       duplexSetting = kPMDuplexNone;
       break;
+    default:  // UNKNOWN_DUPLEX_MODE
+      return true;
   }
 
   PMPrintSettings pmPrintSettings =
diff --git a/printing/printing_context_win.cc b/printing/printing_context_win.cc
index a098a66..c467457 100644
--- a/printing/printing_context_win.cc
+++ b/printing/printing_context_win.cc
@@ -383,9 +383,11 @@ PrintingContext::Result PrintingContextWin::UpdatePrinterSettings(
     case SHORT_EDGE:
       dev_mode->dmDuplex = DMDUP_HORIZONTAL;
       break;
-    default:  // simplex
+    case SIMPLEX:
       dev_mode->dmDuplex = DMDUP_SIMPLEX;
       break;
+    default:  // UNKNOWN_DUPLEX_MODE
+      break;
   }
   dev_mode->dmOrientation = landscape ? DMORIENT_LANDSCAPE : DMORIENT_PORTRAIT;