diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -278,6 +278,8 @@
   DefaultError;
 def err_invalid_macos_32bit_deployment_target : Error<
   "32-bit targets are not supported when building for Mac Catalyst">;
+def err_invalid_ssp_buffer_size : Error<
+  "ssp buffer size is not valid">;
 def err_drv_invalid_os_in_arg : Error<"invalid OS value '%0' in '%1'">;
 def err_drv_conflicting_deployment_targets : Error<
   "conflicting deployment targets, both '%0' and '%1' are present in environment">;
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
@@ -3187,14 +3187,27 @@
     CmdArgs.push_back(Args.MakeArgString(Twine(StackProtectorLevel)));
   }
 
+  auto IsInteger = [](StringRef Str) -> bool {
+    if (Str.empty())
+      return false;
+    for (auto &Chr : Str)
+      if (Chr < '0' || Chr > '9')
+        return false;
+    return true;
+  };
+
   // --param ssp-buffer-size=
   for (const Arg *A : Args.filtered(options::OPT__param)) {
     StringRef Str(A->getValue());
-    if (Str.startswith("ssp-buffer-size=")) {
+    auto StrSplit = Str.split('=');
+    if (StrSplit.first.equals("ssp-buffer-size")) {
       if (StackProtectorLevel) {
-        CmdArgs.push_back("-stack-protector-buffer-size");
-        // FIXME: Verify the argument is a valid integer.
-        CmdArgs.push_back(Args.MakeArgString(Str.drop_front(16)));
+        if (IsInteger(StrSplit.second)) {
+          CmdArgs.push_back("-stack-protector-buffer-size");
+          CmdArgs.push_back(Args.MakeArgString(StrSplit.second));
+        } else {
+          D.Diag(clang::diag::err_invalid_ssp_buffer_size);
+        }
       }
       A->claim();
     }