Index: clang/lib/Driver/Driver.cpp
===================================================================
--- clang/lib/Driver/Driver.cpp
+++ clang/lib/Driver/Driver.cpp
@@ -600,8 +600,9 @@
 
   StringRef LTOName("full");
 
-  const Arg *A = Args.getLastArg(OptEq);
-  if (A)
+  const Arg *A = Args.getLastArg(OptEq, OptPos);
+  // Use the OptEq only if it is after the -flto option.
+  if (A && A->getOption().matches(OptEq))
     LTOName = A->getValue();
 
   LTOMode = llvm::StringSwitch<LTOKind>(LTOName)
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -4492,14 +4492,13 @@
 
     if (IsUsingLTO) {
       if (!IsDeviceOffloadAction) {
-        if (Args.hasArg(options::OPT_flto))
+        Arg *A = Args.getLastArg(options::OPT_flto, options::OPT_flto_EQ);
+        if (A && A->getOption().matches(options::OPT_flto))
           CmdArgs.push_back("-flto");
-        else {
-          if (D.getLTOMode() == LTOK_Thin)
-            CmdArgs.push_back("-flto=thin");
-          else
-            CmdArgs.push_back("-flto=full");
-        }
+        else if (D.getLTOMode() == LTOK_Thin)
+          CmdArgs.push_back("-flto=thin");
+        else
+          CmdArgs.push_back("-flto=full");
         CmdArgs.push_back("-flto-unit");
       } else if (Triple.isAMDGPU()) {
         // Only AMDGPU supports device-side LTO
Index: clang/test/Driver/lto.c
===================================================================
--- clang/test/Driver/lto.c
+++ clang/test/Driver/lto.c
@@ -85,3 +85,15 @@
 // FLTO-AUTO: -flto=full
 // FLTO-JOBSERVER: -flto=full
 //
+
+// Pass the last -flto argument
+// RUN: %clang -target x86_64-unknown-linux -### %s -flto -flto=thin 2>&1 | \
+// RUN: FileCheck --check-prefix=FLTO-THIN %s
+// RUN: %clang -target x86_64-unknown-linux -### %s -flto=thin -flto=full 2>&1 | \
+// RUN: FileCheck --check-prefix=FLTO-FULL %s
+// RUN: %clang -target x86_64-unknown-linux -### %s -flto=thin -flto 2>&1 | \
+// RUN: FileCheck --check-prefix=FLTO %s
+//
+// FLTO-THIN: -flto=thin
+// FLTO-FULL: -flto=full
+// FLTO: "-flto"