Index: llvm/test/tools/llvm-nm/warn-invalid-stdin.test
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-nm/warn-invalid-stdin.test
@@ -0,0 +1,7 @@
+## Tests that when no input file is specified stdin is
+## read but only when not reading from keyoard input.
+
+# RUN: not llvm-nm 2>&1 | FileCheck %s
+
+# CHECK: llvm-nm: warning: can't read from keyboard input.
+# CHECK-NEXT: OVERVIEW: llvm symbol table dumper
Index: llvm/tools/llvm-nm/llvm-nm.cpp
===================================================================
--- llvm/tools/llvm-nm/llvm-nm.cpp
+++ llvm/tools/llvm-nm/llvm-nm.cpp
@@ -34,6 +34,7 @@
 #include "llvm/Support/Format.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Process.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/TargetSelect.h"
@@ -1751,6 +1752,12 @@
 }
 
 static void dumpSymbolNamesFromFile(std::string &Filename) {
+  if (sys::Process::StandardInIsUserInput()) {
+    WithColor::warning(outs(), ToolName) << "can't read from keyboard input.\n";
+    cl::PrintHelpMessage();
+    HadError = true;
+    return;
+  }
   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
       MemoryBuffer::getFileOrSTDIN(Filename);
   if (error(BufferOrErr.getError(), Filename))
@@ -2082,7 +2089,7 @@
   if (OutputFormat == sysv || SizeSort)
     PrintSize = true;
   if (InputFilenames.empty())
-    InputFilenames.push_back("a.out");
+    InputFilenames.push_back("-");
   if (InputFilenames.size() > 1)
     MultipleFiles = true;