diff --git a/clang/include/clang/Basic/LangOptions.h b/clang/include/clang/Basic/LangOptions.h
--- a/clang/include/clang/Basic/LangOptions.h
+++ b/clang/include/clang/Basic/LangOptions.h
@@ -57,7 +57,7 @@
   using RoundingMode = llvm::RoundingMode;
 
   enum GCMode { NonGC, GCOnly, HybridGC };
-  enum StackProtectorMode { SSPOff, SSPOn, SSPStrong, SSPReq };
+  enum StackProtectorMode { SSPOff, SSPOn, SSPStrong, SSPReq, SSPUnspecified };
 
   // Automatic variables live on the stack, and when trivial they're usually
   // uninitialized because it's undefined behavior to use them without
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -309,7 +309,7 @@
         "apply global symbol visibility to external declarations without an explicit visibility")
 BENIGN_LANGOPT(SemanticInterposition        , 1, 0, "semantic interposition")
 BENIGN_LANGOPT(ExplicitNoSemanticInterposition, 1, 0, "explicitly no semantic interposition")
-ENUM_LANGOPT(StackProtector, StackProtectorMode, 2, SSPOff,
+ENUM_LANGOPT(StackProtector, StackProtectorMode, 3, SSPUnspecified,
              "stack protector mode")
 ENUM_LANGOPT(TrivialAutoVarInit, TrivialAutoVarInitKind, 2, TrivialAutoVarInitKind::Uninitialized,
              "trivial automatic variable initialization")
diff --git a/clang/include/clang/Driver/ToolChain.h b/clang/include/clang/Driver/ToolChain.h
--- a/clang/include/clang/Driver/ToolChain.h
+++ b/clang/include/clang/Driver/ToolChain.h
@@ -385,7 +385,7 @@
   /// this tool chain.
   virtual LangOptions::StackProtectorMode
   GetDefaultStackProtectorLevel(bool KernelOrKext) const {
-    return LangOptions::SSPOff;
+    return LangOptions::SSPUnspecified;
   }
 
   /// Get the default trivial automatic variable initialization.
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2994,8 +2994,8 @@
   if (EffectiveTriple.isNVPTX())
     return;
 
-  // -stack-protector=0 is default.
-  LangOptions::StackProtectorMode StackProtectorLevel = LangOptions::SSPOff;
+  LangOptions::StackProtectorMode StackProtectorLevel =
+      LangOptions::SSPUnspecified;
   LangOptions::StackProtectorMode DefaultStackProtectorLevel =
       TC.GetDefaultStackProtectorLevel(KernelOrKext);
 
@@ -3004,8 +3004,11 @@
                                options::OPT_fstack_protector_strong,
                                options::OPT_fstack_protector)) {
     if (A->getOption().matches(options::OPT_fstack_protector))
-      StackProtectorLevel =
-          std::max<>(LangOptions::SSPOn, DefaultStackProtectorLevel);
+      if (DefaultStackProtectorLevel == LangOptions::SSPUnspecified)
+        StackProtectorLevel = LangOptions::SSPOn;
+      else
+        StackProtectorLevel =
+            std::max<>(LangOptions::SSPOn, DefaultStackProtectorLevel);
     else if (A->getOption().matches(options::OPT_fstack_protector_strong))
       StackProtectorLevel = LangOptions::SSPStrong;
     else if (A->getOption().matches(options::OPT_fstack_protector_all))
@@ -3014,7 +3017,7 @@
     StackProtectorLevel = DefaultStackProtectorLevel;
   }
 
-  if (StackProtectorLevel) {
+  if (StackProtectorLevel != LangOptions::SSPUnspecified) {
     CmdArgs.push_back("-stack-protector");
     CmdArgs.push_back(Args.MakeArgString(Twine(StackProtectorLevel)));
   }
diff --git a/clang/lib/Driver/ToolChains/CrossWindows.h b/clang/lib/Driver/ToolChains/CrossWindows.h
--- a/clang/lib/Driver/ToolChains/CrossWindows.h
+++ b/clang/lib/Driver/ToolChains/CrossWindows.h
@@ -62,7 +62,7 @@
 
   LangOptions::StackProtectorMode
   GetDefaultStackProtectorLevel(bool KernelOrKext) const override {
-    return LangOptions::SSPOff;
+    return LangOptions::SSPUnspecified;
   }
 
   void
diff --git a/clang/lib/Driver/ToolChains/Darwin.h b/clang/lib/Driver/ToolChains/Darwin.h
--- a/clang/lib/Driver/ToolChains/Darwin.h
+++ b/clang/lib/Driver/ToolChains/Darwin.h
@@ -503,7 +503,7 @@
     else if (isTargetMacOS() && !isMacosxVersionLT(10, 5) && !KernelOrKext)
       return LangOptions::SSPOn;
 
-    return LangOptions::SSPOff;
+    return LangOptions::SSPUnspecified;
   }
 
   void CheckObjCARC() const override;
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -3379,7 +3379,7 @@
   Opts.RetainCommentsFromSystemHeaders =
       Args.hasArg(OPT_fretain_comments_from_system_headers);
 
-  unsigned SSP = getLastArgIntValue(Args, OPT_stack_protector, 0, Diags);
+  unsigned SSP = getLastArgIntValue(Args, OPT_stack_protector, UINT_MAX, Diags);
   switch (SSP) {
   default:
     Diags.Report(diag::err_drv_invalid_value)
@@ -3389,6 +3389,9 @@
   case 1: Opts.setStackProtector(LangOptions::SSPOn);  break;
   case 2: Opts.setStackProtector(LangOptions::SSPStrong); break;
   case 3: Opts.setStackProtector(LangOptions::SSPReq); break;
+  case UINT_MAX:
+    Opts.setStackProtector(LangOptions::SSPUnspecified);
+    break;
   }
 
   if (Arg *A = Args.getLastArg(OPT_ftrivial_auto_var_init)) {
diff --git a/clang/test/CodeGen/stack-protector.c b/clang/test/CodeGen/stack-protector.c
--- a/clang/test/CodeGen/stack-protector.c
+++ b/clang/test/CodeGen/stack-protector.c
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -emit-llvm -o - %s -stack-protector 0 | FileCheck -check-prefix=DEF -check-prefix=NOSSP %s
+// RUN: %clang_cc1 -emit-llvm -o - %s -stack-protector 0 | FileCheck -check-prefix=DEF-NOSSP -check-prefix=NOSSP %s
 // RUN: %clang_cc1 -emit-llvm -o - %s -stack-protector 1 | FileCheck -check-prefix=DEF -check-prefix=SSP %s
 // RUN: %clang_cc1 -emit-llvm -o - %s -stack-protector 2 | FileCheck -check-prefix=DEF -check-prefix=SSPSTRONG %s
 // RUN: %clang_cc1 -emit-llvm -o - %s -stack-protector 3 | FileCheck -check-prefix=DEF -check-prefix=SSPREQ %s
@@ -16,6 +16,7 @@
 char *strcpy(char *s1, const char *s2);
 
 // DEF: define {{.*}}void @test1(i8* %msg) #[[A:.*]] {
+// DEF-NOSSP: define {{.*}}void @test1(i8* %msg) #[[B:.*]] {
 void test1(const char *msg) {
   char a[strlen(msg) + 1];
   strcpy(a, msg);
@@ -23,6 +24,7 @@
 }
 
 // DEF: define {{.*}}void @test2(i8* %msg) #[[B:.*]] {
+// DEF-NOSSP: define {{.*}}void @test2(i8* %msg) #[[B:.*]] {
 __attribute__((no_stack_protector))
 void test2(const char *msg) {
   char a[strlen(msg) + 1];