Index: llvm/docs/CommandGuide/llvm-nm.rst
===================================================================
--- llvm/docs/CommandGuide/llvm-nm.rst
+++ llvm/docs/CommandGuide/llvm-nm.rst
@@ -14,9 +14,8 @@
 The :program:`llvm-nm` utility lists the names of symbols from the LLVM bitcode
 files, object files, or :program:`ar` archives containing them, named on the
 command line.  Each symbol is listed along with some simple information about
-its provenance.  If no filename is specified, *a.out* is used as the input.
-If *-* is used as a filename, :program:`llvm-nm` will read a file from its
-standard input stream.
+its provenance.  If no filename is specified, or *-* is used as a filename,
+:program:`llvm-nm` will read a file from its standard input stream.
 
 :program:`llvm-nm`'s default output format is the traditional BSD :program:`nm`
 output format.  Each such output record consists of an (optional) 8-digit
Index: llvm/test/tools/llvm-nm/stdin.test
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-nm/stdin.test
@@ -0,0 +1,33 @@
+## Test llvm-nm when using stdin both explicitly (using '-' as a filename)
+## and implicitly (not specifying any filename).
+
+# RUN: yaml2obj %s -o %t.o
+
+## Pass an explicit filename to produce a baseline output. llvm-nm should
+## have the same behavior when opening a file itself and reading that file
+## from its standard input stream.
+# RUN: llvm-nm %t.o > %t.base 2> %t.err
+
+## Make sure there is no warning message about no file redirected to stdin.
+# RUN: FileCheck %s --input-file=%t.err --allow-empty --implicit-check-not={{.}}
+
+# RUN: llvm-nm - < %t.o > %t.explicit 2> %t.err
+# RUN: FileCheck %s --input-file=%t.err --allow-empty --implicit-check-not={{.}}
+# RUN: cmp %t.base %t.explicit
+
+# RUN: llvm-nm < %t.o > %t.implicit 2> %t.err
+# RUN: FileCheck %s --input-file=%t.err --allow-empty --implicit-check-not={{.}}
+# RUN: cmp %t.base %t.implicit
+
+!ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Name: .text
+    Type: SHT_PROGBITS
+Symbols:
+  - Name:    symbol_a
+    Section: .text
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 (Filename == "-" && sys::Process::StandardInIsUserInput()) {
+    WithColor::warning(errs(), 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;