diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index d8af8f34530b..eb0770a952c6 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -3812,7 +3812,8 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
       PendingInstantiations.push_back(
         std::make_pair(Function, PointOfInstantiation));
     } else if (TSK == TSK_ImplicitInstantiation) {
-      if (AtEndOfTU && !getDiagnostics().hasErrorOccurred()) {
+      if (AtEndOfTU && !getDiagnostics().hasErrorOccurred() &&
+          !getSourceManager().isInSystemHeader(PatternDecl->getLocStart())) {
         Diag(PointOfInstantiation, diag::warn_func_template_missing)
           << Function;
         Diag(PatternDecl->getLocation(), diag::note_forward_template_decl);
@@ -4347,7 +4348,8 @@ void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
         std::make_pair(Var, PointOfInstantiation));
     } else if (TSK == TSK_ImplicitInstantiation) {
       // Warn about missing definition at the end of translation unit.
-      if (AtEndOfTU && !getDiagnostics().hasErrorOccurred()) {
+      if (AtEndOfTU && !getDiagnostics().hasErrorOccurred() &&
+          !getSourceManager().isInSystemHeader(PatternDecl->getLocStart())) {
         Diag(PointOfInstantiation, diag::warn_var_template_missing)
           << Var;
         Diag(PatternDecl->getLocation(), diag::note_forward_template_decl);
diff --git a/clang/test/SemaTemplate/undefined-template.cpp b/clang/test/SemaTemplate/undefined-template.cpp
index 7dfe2fde94b0..52530e2e3909 100644
--- a/clang/test/SemaTemplate/undefined-template.cpp
+++ b/clang/test/SemaTemplate/undefined-template.cpp
@@ -1,5 +1,6 @@
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++14 -Wundefined-func-template %s
 
+#if !defined(INCLUDE)
 template <class T> struct C1 {
   static char s_var_1;       // expected-note{{forward declaration of template entity is here}}
   static char s_var_2;       // expected-note{{forward declaration of template entity is here}}
@@ -142,6 +143,16 @@ namespace test_24 {
   void h(X<int> x) { g(x); } // no warning for use of 'g' despite the declaration having been instantiated from a template
 }
 
+#define INCLUDE
+#include "undefined-template.cpp"
+void func_25(SystemHeader<char> *x) {
+  x->meth();
+}
+
 int main() {
   return 0;
 }
+#else
+#pragma clang system_header
+template <typename T> struct SystemHeader { T meth(); };
+#endif