Index: lib/Driver/Driver.cpp
===================================================================
--- lib/Driver/Driver.cpp
+++ lib/Driver/Driver.cpp
@@ -2998,9 +2998,10 @@
     Args.eraseArg(options::OPT__SLASH_Yc);
     YcArg = nullptr;
   }
-  if (Args.hasArg(options::OPT__SLASH_Y_)) {
-    // /Y- disables all pch handling.  Rather than check for it everywhere,
-    // just remove clang-cl pch-related flags here.
+  if (FinalPhase == phases::Preprocess || Args.hasArg(options::OPT__SLASH_Y_)) {
+    // If only preprocessing or /Y- is used, all pch handling is disabled.
+    // Rather than check for it everywhere, just remove clang-cl pch-related
+    // flags here.
     Args.eraseArg(options::OPT__SLASH_Fp);
     Args.eraseArg(options::OPT__SLASH_Yc);
     Args.eraseArg(options::OPT__SLASH_Yu);
Index: test/Driver/cl-pch.cpp
===================================================================
--- test/Driver/cl-pch.cpp
+++ test/Driver/cl-pch.cpp
@@ -345,3 +345,24 @@
 // CHECK-NoSourceTP: pchfile.pch
 // CHECK-NoSourceTP: -x
 // CHECK-NoSourceTP: "c++"
+
+// If only preprocessing, PCH options are ignored.
+// RUN: %clang_cl /P /Ycpchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC-P %s
+// CHECK-YC-P-NOT: -emit-pch
+// CHECK-YC-P-NOT: -include-pch
+
+// RUN: %clang_cl /E /Ycpchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC-E %s
+// CHECK-YC-E-NOT: -emit-pch
+// CHECK-YC-E-NOT: -include-pch
+
+// RUN: %clang_cl /P /Ycpchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YU-P %s
+// CHECK-YU-P-NOT: -emit-pch
+// CHECK-YU-P-NOT: -include-pch
+
+// RUN: %clang_cl /E /Ycpchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YU-E %s
+// CHECK-YU-E-NOT: -emit-pch
+// CHECK-YU-E-NOT: -include-pch
Index: test/PCH/Inputs/pch-through-use3c.cpp
===================================================================
--- /dev/null
+++ test/PCH/Inputs/pch-through-use3c.cpp
@@ -0,0 +1,2 @@
+int a = A;
+// expected-no-diagnostics
Index: test/PCH/Inputs/pch-through3c.h
===================================================================
--- /dev/null
+++ test/PCH/Inputs/pch-through3c.h
@@ -0,0 +1 @@
+#define A 1
Index: test/PCH/pch-through3c.cpp
===================================================================
--- /dev/null
+++ test/PCH/pch-through3c.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -I %S -emit-pch \
+// RUN:   -include Inputs/pch-through3c.h \
+// RUN:   -pch-through-header=Inputs/pch-through3c.h -o %t.3c %s
+
+// RUN: %clang_cc1 -verify -I %S -include-pch %t.3c \
+// RUN:   -include Inputs/pch-through3c.h \
+// RUN:   -pch-through-header=Inputs/pch-through3c.h \
+// RUN:   %S/Inputs/pch-through-use3c.cpp 2>&1