Index: lib/MC/MCParser/AsmParser.cpp
===================================================================
--- lib/MC/MCParser/AsmParser.cpp
+++ lib/MC/MCParser/AsmParser.cpp
@@ -973,6 +973,9 @@
 
     // This is a symbol reference.
     StringRef SymbolName = Identifier;
+    if (SymbolName.empty())
+      return true;
+
     MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
 
     // Lookup the symbol variant if used.
Index: test/MC/AsmParser/equ.s
===================================================================
--- test/MC/AsmParser/equ.s
+++ test/MC/AsmParser/equ.s
@@ -5,5 +5,6 @@
 .set	a, 1
 .equ	a, 2
 .equiv	a, 3
+.set  b, ""
 // CHECK: error: redefinition of 'a'
-
+// CHECK: error: missing expression in '.set' directive