diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -14154,11 +14154,7 @@
       //   Warn if K&R function is defined without a previous declaration.
       //   This warning is issued only if the definition itself does not provide
       //   a prototype. Only K&R definitions do not provide a prototype.
-      //   An empty list in a function declarator that is part of a definition
-      //   of that function specifies that the function has no parameters
-      //   (C99 6.7.5.3p14)
-      if (!FD->hasWrittenPrototype() && FD->getNumParams() > 0 &&
-          !LangOpts.CPlusPlus) {
+      if (!FD->hasWrittenPrototype()) {
         TypeSourceInfo *TI = FD->getTypeSourceInfo();
         TypeLoc TL = TI->getTypeLoc();
         FunctionTypeLoc FTL = TL.getAsAdjusted<FunctionTypeLoc>();
diff --git a/clang/test/Sema/warn-strict-prototypes.c b/clang/test/Sema/warn-strict-prototypes.c
--- a/clang/test/Sema/warn-strict-prototypes.c
+++ b/clang/test/Sema/warn-strict-prototypes.c
@@ -1,15 +1,18 @@
 // RUN: %clang_cc1 -triple i386-pc-unknown -fsyntax-only -Wstrict-prototypes -Wno-implicit-function-declaration -verify %s
 // RUN: %clang_cc1 -triple i386-pc-unknown -fsyntax-only -Wstrict-prototypes -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
 
+// function definition with 0 params, no prototype, no preceding declaration.
+void foo0() {} // expected-warning {{this old-style function definition is not preceded by a prototype}}
+
 // function declaration with unspecified params
 void foo1(); // expected-warning {{this function declaration is not a prototype}}
              // CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:11-[[@LINE-1]]:11}:"void"
 // function declaration with 0 params
 void foo2(void);
 
-// function definition with 0 params(for both cases),
-// valid according to 6.7.5.3/14
-void foo1() {}
+// function definition with 0 params, no prototype.
+void foo1() {} // expected-warning {{this old-style function definition is not preceded by a prototype}}
+// function definition with 0 params, prototype.
 void foo2(void) {}
 
 // function type typedef unspecified params
diff --git a/clang/test/Sema/warn-strict-prototypes.cpp b/clang/test/Sema/warn-strict-prototypes.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Sema/warn-strict-prototypes.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -verify -fsyntax-only -Wstrict-prototypes %s
+// expected-no-diagnostics
+
+void decl();
+void decl_void(void);
+
+void def() {}
+void def_void(void) {}
diff --git a/clang/test/Sema/warn-strict-prototypes.m b/clang/test/Sema/warn-strict-prototypes.m
--- a/clang/test/Sema/warn-strict-prototypes.m
+++ b/clang/test/Sema/warn-strict-prototypes.m
@@ -10,7 +10,7 @@
 
 @end
 
-void foo() {
+void foo() { // expected-warning {{this old-style function definition is not preceded by a prototype}}
   void (^block)() = // expected-warning {{this block declaration is not a prototype}}
                     ^void(int arg) { // no warning
   };