Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -11805,7 +11805,11 @@
       prev = prev->getPreviousDecl();
 
     if (!prev)
-      Diag(var->getLocation(), diag::warn_missing_variable_declarations) << var;
+      Diag(var->getLocation(), diag::warn_missing_variable_declarations)
+          << var
+          << ((var->getStorageClass() != SC_Extern)
+                  ? FixItHint::CreateInsertion(var->getBeginLoc(), "static ")
+                  : FixItHint{});
   }
 
   // Cache the result of checking for constant initialization.
@@ -13209,7 +13213,11 @@
     //   global functions that fail to be declared in header files.
     const FunctionDecl *PossibleZeroParamPrototype = nullptr;
     if (ShouldWarnAboutMissingPrototype(FD, PossibleZeroParamPrototype)) {
-      Diag(FD->getLocation(), diag::warn_missing_prototype) << FD;
+      Diag(FD->getLocation(), diag::warn_missing_prototype)
+          << FD
+          << ((FD->getStorageClass() != SC_Extern)
+                  ? FixItHint::CreateInsertion(FD->getBeginLoc(), "static ")
+                  : FixItHint{});
 
       if (PossibleZeroParamPrototype) {
         // We found a declaration that is not a prototype,
Index: test/Sema/warn-missing-prototypes.c
===================================================================
--- test/Sema/warn-missing-prototypes.c
+++ test/Sema/warn-missing-prototypes.c
@@ -4,6 +4,7 @@
 int f();
 
 int f(int x) { return x; } // expected-warning{{no previous prototype for function 'f'}}
+// CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:1-[[@LINE-1]]:1}:"static "
 
 static int g(int x) { return x; }
 
@@ -13,6 +14,9 @@
 
 int g2(int x) { return x; }
 
+extern int g3(int x) { return x; } // expected-warning{{no previous prototype for function 'g3'}}
+// CHECK-NOT: fix-it:"{{.*}}":{[[@LINE-1]]{{.*}}}:"{{.*}}"
+
 void test(void);
 
 int h3();
@@ -40,4 +44,4 @@
 void not_a_prototype_test(); // expected-note{{this declaration is not a prototype; add 'void' to make it a prototype for a zero-parameter function}}
 void not_a_prototype_test() { } // expected-warning{{no previous prototype for function 'not_a_prototype_test'}}
 
-// CHECK: fix-it:"{{.*}}":{40:27-40:27}:"void"
+// CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:27-[[@LINE-3]]:27}:"void"
Index: test/Sema/warn-missing-variable-declarations.c
===================================================================
--- test/Sema/warn-missing-variable-declarations.c
+++ test/Sema/warn-missing-variable-declarations.c
@@ -1,6 +1,8 @@
 // RUN: %clang_cc1 -Wmissing-variable-declarations -fsyntax-only -verify %s
+// RUN: %clang_cc1 -fsyntax-only -Wmissing-variable-declarations -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
 
 int vbad1; // expected-warning{{no previous extern declaration for non-static variable 'vbad1'}}
+// CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:1-[[@LINE-1]]:1}:"static "
 
 int vbad2;
 int vbad2 = 10; // expected-warning{{no previous extern declaration for non-static variable 'vbad2'}}
@@ -8,6 +10,7 @@
 struct {
   int mgood1;
 } vbad3; // expected-warning{{no previous extern declaration for non-static variable 'vbad3'}}
+// CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:1-[[@LINE-3]]:1}:"static "
 
 int vbad4;
 int vbad4 = 10; // expected-warning{{no previous extern declaration for non-static variable 'vbad4'}}
Index: test/SemaCXX/warn-missing-variable-declarations.cpp
===================================================================
--- test/SemaCXX/warn-missing-variable-declarations.cpp
+++ test/SemaCXX/warn-missing-variable-declarations.cpp
@@ -1,11 +1,15 @@
-// RUN: %clang -Wmissing-variable-declarations -fsyntax-only -Xclang -verify -std=c++17 %s
+// RUN: %clang_cc1 -fsyntax-only -verify -Wmissing-variable-declarations -std=c++17 %s
+// RUN: %clang_cc1 -fsyntax-only -Wmissing-variable-declarations -fdiagnostics-parseable-fixits -std=c++17 %s 2>&1 | FileCheck %s
 
 // Variable declarations that should trigger a warning.
 int vbad1; // expected-warning{{no previous extern declaration for non-static variable 'vbad1'}}
+// CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:1-[[@LINE-1]]:1}:"static "
 int vbad2 = 10; // expected-warning{{no previous extern declaration for non-static variable 'vbad2'}}
+// CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:1-[[@LINE-1]]:1}:"static "
 
 namespace x {
   int vbad3; // expected-warning{{no previous extern declaration for non-static variable 'vbad3'}}
+  // CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:3-[[@LINE-1]]:3}:"static "
 }
 
 // Variable declarations that should not trigger a warning.
@@ -58,7 +62,9 @@
 constexpr int constexpr_var = 0;
 inline constexpr int inline_constexpr_var = 0;
 extern const int extern_const_var = 0; // expected-warning {{no previous extern declaration}}
+// CHECK-NOT: fix-it:"{{.*}}":{[[@LINE-1]]{{.*}}}:"{{.*}}"
 extern constexpr int extern_constexpr_var = 0; // expected-warning {{no previous extern declaration}}
+// CHECK-NOT: fix-it:"{{.*}}":{[[@LINE-1]]{{.*}}}:"{{.*}}"
 
 template<typename> int var_template = 0;
 template<typename> constexpr int const_var_template = 0;