Index: lld/trunk/COFF/Driver.cpp
===================================================================
--- lld/trunk/COFF/Driver.cpp
+++ lld/trunk/COFF/Driver.cpp
@@ -137,9 +137,6 @@
       fatal(MBOrErr.second, "could not open " + PathStr);
     Driver->addBuffer(std::move(MBOrErr.first));
   });
-
-  if (Config->OutputFile == "")
-    Config->OutputFile = getOutputPath(Path);
 }
 
 void LinkerDriver::addArchiveBuffer(MemoryBufferRef MB, StringRef SymName,
@@ -887,6 +884,12 @@
     }
   }
 
+  // Set default image name if neither /out or /def set it.
+  if (Config->OutputFile.empty()) {
+    Config->OutputFile =
+        getOutputPath((*Args.filtered_begin(OPT_INPUT))->getValue());
+  }
+
   // Set default image base if /base is not given.
   if (Config->ImageBase == uint64_t(-1))
     Config->ImageBase = getDefaultImageBase();
Index: lld/trunk/COFF/ModuleDef.cpp
===================================================================
--- lld/trunk/COFF/ModuleDef.cpp
+++ lld/trunk/COFF/ModuleDef.cpp
@@ -163,17 +163,25 @@
     case KwHeapsize:
       parseNumbers(&Config->HeapReserve, &Config->HeapCommit);
       return;
-    case KwLibrary:
-      parseName(&Config->OutputFile, &Config->ImageBase);
-      if (!StringRef(Config->OutputFile).endswith_lower(".dll"))
-        Config->OutputFile += ".dll";
-      return;
     case KwStacksize:
       parseNumbers(&Config->StackReserve, &Config->StackCommit);
       return;
-    case KwName:
-      parseName(&Config->OutputFile, &Config->ImageBase);
+    case KwLibrary:
+    case KwName: {
+      bool IsDll = Tok.K == KwLibrary; // Check before parseName.
+      std::string Name;
+      parseName(&Name, &Config->ImageBase);
+
+      // Append the appropriate file extension if not already present.
+      StringRef Ext = IsDll ? ".dll" : ".exe";
+      if (!StringRef(Name).endswith_lower(Ext))
+        Name += Ext;
+
+      // Set the output file, but don't override /out if it was already passed.
+      if (Config->OutputFile.empty())
+        Config->OutputFile = Name;
       return;
+    }
     case KwVersion:
       parseVersion(&Config->MajorImageVersion, &Config->MinorImageVersion);
       return;
Index: lld/trunk/test/COFF/def-name.test
===================================================================
--- lld/trunk/test/COFF/def-name.test
+++ lld/trunk/test/COFF/def-name.test
@@ -0,0 +1,28 @@
+# REQUIRES: winres
+
+# RUN: rm -rf %t
+# RUN: mkdir -p %t
+# RUN: cd %t
+# RUN: yaml2obj < %p/Inputs/ret42.yaml > in.obj
+
+# RUN: lld-link /entry:main in.obj
+# RUN: lld-link /entry:main /dll in.obj
+
+# RUN: echo -e "NAME foo\n" > fooexe.def
+# RUN: echo -e "LIBRARY foo\n" > foodll.def
+# RUN: lld-link /entry:main /def:fooexe.def in.obj
+# RUN: lld-link /entry:main /def:foodll.def /dll in.obj
+
+# RUN: lld-link /entry:main /out:bar.exe /def:fooexe.def in.obj
+# RUN: lld-link /entry:main /out:bar.dll /def:foodll.def /dll in.obj
+
+# RUN: llvm-readobj in.exe | FileCheck %s
+# RUN: llvm-readobj in.dll | FileCheck %s
+
+# RUN: llvm-readobj foo.exe | FileCheck %s
+# RUN: llvm-readobj foo.dll | FileCheck %s
+
+# RUN: llvm-readobj bar.exe | FileCheck %s
+# RUN: llvm-readobj bar.dll | FileCheck %s
+
+CHECK: File: