diff --git a/lib/MC/MCELFStreamer.cpp b/lib/MC/MCELFStreamer.cpp
index 9249d9c49b6..3be9ed5f6d7 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:
-    llvm_unreachable("ELF doesn't support this attribute");
+    report_fatal_error("ELF doesn't support the .alt_entry attribute");
   }
 
   return true;
diff --git a/lib/MC/WinCOFFStreamer.cpp b/lib/MC/WinCOFFStreamer.cpp
index f9d231921d5..a2dda36bbea 100644
--- a/lib/MC/WinCOFFStreamer.cpp
+++ b/lib/MC/WinCOFFStreamer.cpp
@@ -107,6 +107,8 @@ bool MCWinCOFFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
   case MCSA_Global:
     Symbol->setExternal(true);
     break;
+  case MCSA_AltEntry:
+    report_fatal_error("COFF doesn't support the .alt_entry attribute");
   }
 
   return true;