Index: test/Sema/exprs.c
===================================================================
--- test/Sema/exprs.c	(revision 156464)
+++ test/Sema/exprs.c	(working copy)
@@ -162,11 +162,15 @@
   x = sizeof(x/0);  // no warning.
 }
 
-// PR6501
+// PR6501 & PR11857
 void test18_a(int a); // expected-note 2 {{'test18_a' declared here}}
+void test18_b(int); // expected-note {{'test18_b' declared here}}
+void test18_c(int a, int b); // expected-note {{'test18_c' declared here}}
 void test18(int b) {
   test18_a(b, b); // expected-error {{too many arguments to function call, expected 1, have 2}}
-  test18_a(); // expected-error {{too few arguments to function call, expected 1, have 0}}
+  test18_a(); // expected-error {{too few arguments to function call, argument 'a' was not specified}}
+  test18_b(); // expected-error {{too few arguments to function call, expected 1, have 0}}
+  test18_c(b); // expected-error {{too few arguments to function call, expected 2, have 1}}
 }
 
 // PR7569
Index: test/SemaCXX/default1.cpp
===================================================================
--- test/SemaCXX/default1.cpp	(revision 156464)
+++ test/SemaCXX/default1.cpp	(working copy)
@@ -47,6 +47,6 @@
   void j (int f = 4);
   {
     void j (int f); // expected-note{{'j' declared here}}
-    j(); // expected-error{{too few arguments to function call, expected 1, have 0}}
+    j(); // expected-error{{too few arguments to function call, argument 'f' was not specified}}
   }
 }
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td	(revision 156464)
+++ include/clang/Basic/DiagnosticSemaKinds.td	(working copy)
@@ -4558,10 +4558,18 @@
   "too few %select{|||execution configuration }0arguments to "
   "%select{function|block|method|kernel function}0 call, "
   "expected %1, have %2">;
+def err_typecheck_call_too_few_args_one : Error<
+  "too few %select{|||execution configuration }0arguments to "
+  "%select{function|block|method|kernel function}0 call, "
+  "argument '%1' was not specified">;
 def err_typecheck_call_too_few_args_at_least : Error<
   "too few %select{|||execution configuration }0arguments to "
   "%select{function|block|method|kernel function}0 call, "
   "expected at least %1, have %2">;
+def err_typecheck_call_too_few_args_at_least_one : Error<
+  "too few %select{|||execution configuration }0arguments to "
+  "%select{function|block|method|kernel function}0 call, "
+  "at least argument '%1' must be specified">;
 def err_typecheck_call_too_many_args : Error<
   "too many %select{|||execution configuration }0arguments to "
   "%select{function|block|method|kernel function}0 call, "
Index: lib/Sema/SemaExpr.cpp
===================================================================
--- lib/Sema/SemaExpr.cpp	(revision 156464)
+++ lib/Sema/SemaExpr.cpp	(working copy)
@@ -3380,11 +3380,18 @@
   // arguments for the remaining parameters), don't make the call.
   if (NumArgs < NumArgsInProto) {
     if (NumArgs < MinArgs) {
-      Diag(RParenLoc, MinArgs == NumArgsInProto
-                        ? diag::err_typecheck_call_too_few_args
-                        : diag::err_typecheck_call_too_few_args_at_least)
-        << FnKind
-        << MinArgs << NumArgs << Fn->getSourceRange();
+      if (MinArgs == 1 && FDecl && !FDecl->getParamDecl(0)->getName().empty())
+        Diag(RParenLoc, MinArgs == NumArgsInProto
+                          ? diag::err_typecheck_call_too_few_args_one
+                          : diag::err_typecheck_call_too_few_args_at_least_one)
+          << FnKind
+          << FDecl->getParamDecl(0)->getNameAsString() << Fn->getSourceRange();
+      else
+        Diag(RParenLoc, MinArgs == NumArgsInProto
+                          ? diag::err_typecheck_call_too_few_args
+                          : diag::err_typecheck_call_too_few_args_at_least)
+          << FnKind
+          << MinArgs << NumArgs << Fn->getSourceRange();
 
       // Emit the location of the prototype.
       if (FDecl && !FDecl->getBuiltinID() && !IsExecConfig)