diff --git a/lib/MC/MCELFStreamer.cpp b/lib/MC/MCELFStreamer.cpp
index 3be9ed5f6d7..1000da9e766 100644
--- a/lib/MC/MCELFStreamer.cpp
+++ b/lib/MC/MCELFStreamer.cpp
@@ -285,7 +285,7 @@ bool MCELFStreamer::EmitSymbolAttribute(MCSymbol *S, MCSymbolAttr Attribute) {
     break;
 
   case MCSA_AltEntry:
-    report_fatal_error("ELF doesn't support the .alt_entry attribute");
+    llvm_unreachable("ELF doesn't support the .alt_entry attribute");
   }
 
   return true;
diff --git a/lib/MC/MCParser/AsmParser.cpp b/lib/MC/MCParser/AsmParser.cpp
index fef6bb6b641..c7763fe7d63 100644
--- a/lib/MC/MCParser/AsmParser.cpp
+++ b/lib/MC/MCParser/AsmParser.cpp
@@ -350,7 +350,7 @@ private:
     DK_BALIGNL, DK_P2ALIGN, DK_P2ALIGNW, DK_P2ALIGNL, DK_ORG, DK_FILL, DK_ENDR,
     DK_BUNDLE_ALIGN_MODE, DK_BUNDLE_LOCK, DK_BUNDLE_UNLOCK,
     DK_ZERO, DK_EXTERN, DK_GLOBL, DK_GLOBAL,
-    DK_LAZY_REFERENCE, DK_NO_DEAD_STRIP, DK_SYMBOL_RESOLVER, DK_ALT_ENTRY,
+    DK_LAZY_REFERENCE, DK_NO_DEAD_STRIP, DK_SYMBOL_RESOLVER,
     DK_PRIVATE_EXTERN, DK_REFERENCE, DK_WEAK_DEFINITION, DK_WEAK_REFERENCE,
     DK_WEAK_DEF_CAN_BE_HIDDEN, DK_COMM, DK_COMMON, DK_LCOMM, DK_ABORT,
     DK_INCLUDE, DK_INCBIN, DK_CODE16, DK_CODE16GCC, DK_REPT, DK_IRP, DK_IRPC,
@@ -1598,8 +1598,6 @@ bool AsmParser::parseStatement(ParseStatementInfo &Info,
       return parseDirectiveSymbolAttribute(MCSA_NoDeadStrip);
     case DK_SYMBOL_RESOLVER:
       return parseDirectiveSymbolAttribute(MCSA_SymbolResolver);
-    case DK_ALT_ENTRY:
-      return parseDirectiveSymbolAttribute(MCSA_AltEntry);
     case DK_PRIVATE_EXTERN:
       return parseDirectiveSymbolAttribute(MCSA_PrivateExtern);
     case DK_REFERENCE:
@@ -4627,7 +4625,6 @@ void AsmParser::initializeDirectiveKindMap() {
   DirectiveKindMap[".lazy_reference"] = DK_LAZY_REFERENCE;
   DirectiveKindMap[".no_dead_strip"] = DK_NO_DEAD_STRIP;
   DirectiveKindMap[".symbol_resolver"] = DK_SYMBOL_RESOLVER;
-  DirectiveKindMap[".alt_entry"] = DK_ALT_ENTRY;
   DirectiveKindMap[".private_extern"] = DK_PRIVATE_EXTERN;
   DirectiveKindMap[".reference"] = DK_REFERENCE;
   DirectiveKindMap[".weak_definition"] = DK_WEAK_DEFINITION;
diff --git a/lib/MC/MCParser/DarwinAsmParser.cpp b/lib/MC/MCParser/DarwinAsmParser.cpp
index 73e068a3439..f033a1dfc7e 100644
--- a/lib/MC/MCParser/DarwinAsmParser.cpp
+++ b/lib/MC/MCParser/DarwinAsmParser.cpp
@@ -50,6 +50,7 @@ public:
     // Call the base implementation.
     this->MCAsmParserExtension::Initialize(Parser);
 
+    addDirectiveHandler<&DarwinAsmParser::parseDirectiveAltEntry>(".alt_entry");
     addDirectiveHandler<&DarwinAsmParser::parseDirectiveDesc>(".desc");
     addDirectiveHandler<&DarwinAsmParser::parseDirectiveIndirectSymbol>(
       ".indirect_symbol");
@@ -179,6 +180,7 @@ public:
     LastVersionMinDirective = SMLoc();
   }
 
+  bool parseDirectiveAltEntry(StringRef, SMLoc);
   bool parseDirectiveDesc(StringRef, SMLoc);
   bool parseDirectiveIndirectSymbol(StringRef, SMLoc);
   bool parseDirectiveDumpOrLoad(StringRef, SMLoc);
@@ -408,6 +410,26 @@ bool DarwinAsmParser::parseSectionSwitch(const char *Segment,
   return false;
 }
 
+/// parseDirectiveAltEntry
+///  ::= .alt_entry identifier
+bool DarwinAsmParser::parseDirectiveAltEntry(StringRef, SMLoc) {
+  StringRef Name;
+  if (getParser().parseIdentifier(Name))
+    return TokError("expected identifier in directive");
+
+  // Look up symbol.
+  MCSymbol *Sym = getContext().getOrCreateSymbol(Name);
+
+  if (Sym->isDefined())
+    return TokError(".alt_entry must preceed symbol definition");
+
+  if (!getStreamer().EmitSymbolAttribute(Sym, MCSA_AltEntry))
+    return TokError("unable to emit symbol attribute");
+
+  Lex();
+  return false;
+}
+
 /// parseDirectiveDesc
 ///  ::= .desc identifier , expression
 bool DarwinAsmParser::parseDirectiveDesc(StringRef, SMLoc) {
diff --git a/lib/MC/WinCOFFStreamer.cpp b/lib/MC/WinCOFFStreamer.cpp
index a2dda36bbea..312cebf9589 100644
--- a/lib/MC/WinCOFFStreamer.cpp
+++ b/lib/MC/WinCOFFStreamer.cpp
@@ -108,7 +108,7 @@ bool MCWinCOFFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
     Symbol->setExternal(true);
     break;
   case MCSA_AltEntry:
-    report_fatal_error("COFF doesn't support the .alt_entry attribute");
+    llvm_unreachable("COFF doesn't support the .alt_entry attribute");
   }
 
   return true;