Index: clang/lib/Sema/SemaType.cpp
===================================================================
--- clang/lib/Sema/SemaType.cpp
+++ clang/lib/Sema/SemaType.cpp
@@ -5109,7 +5109,7 @@
             // is an incomplete type (C99 6.2.5p19) and function decls cannot
             // have parameters of incomplete type.
             if (FTI.NumParams != 1 || FTI.isVariadic) {
-              S.Diag(DeclType.Loc, diag::err_void_only_param);
+              S.Diag(FTI.Params[i].IdentLoc, diag::err_void_only_param);
               ParamTy = Context.IntTy;
               Param->setType(ParamTy);
             } else if (FTI.Params[i].Ident) {
Index: clang/test/Sema/void-argument.cpp
===================================================================
--- /dev/null
+++ clang/test/Sema/void-argument.cpp
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+void foo(
+    void a, // expected-error{{'void' must be the first and only parameter if specified}}
+    double b,
+    int c,
+    void d, // expected-error{{'void' must be the first and only parameter if specified}}
+    int e,
+    void f) // expected-error{{'void' must be the first and only parameter if specified}}
+{}
Index: clang/test/Sema/void-unnamed.cpp
===================================================================
--- /dev/null
+++ clang/test/Sema/void-unnamed.cpp
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+void foo(
+    int a,
+    void, // expected-error{{'void' must be the first and only parameter if specified}}
+    int b);
+
+void bar(
+    void, // expected-error{{'void' must be the first and only parameter if specified}}
+    ...);
+
+struct S {
+  S(
+      void,  // expected-error{{'void' must be the first and only parameter if specified}}
+      void); // expected-error{{'void' must be the first and only parameter if specified}}
+};