Index: lib/MC/MCParser/AsmParser.cpp
===================================================================
--- lib/MC/MCParser/AsmParser.cpp
+++ lib/MC/MCParser/AsmParser.cpp
@@ -5035,9 +5035,9 @@
     MCSymbol *Sym = getContext().lookupSymbol(Name);
 
     if (expect_defined)
-      TheCondState.CondMet = (Sym && !Sym->isUndefined());
+      TheCondState.CondMet = (Sym && !Sym->isUndefined(false));
     else
-      TheCondState.CondMet = (!Sym || Sym->isUndefined());
+      TheCondState.CondMet = (!Sym || Sym->isUndefined(false));
     TheCondState.Ignore = !TheCondState.CondMet;
   }
 
Index: test/MC/AsmParser/ifdef.s
===================================================================
--- test/MC/AsmParser/ifdef.s
+++ test/MC/AsmParser/ifdef.s
@@ -27,3 +27,13 @@
 .else
 	.byte 1
 .endif
+
+# .ifdef directive does not count as a use, so ensure redefinition is permitted
+.set var, 1
+.ifdef var
+	.set var, 2
+.else
+	.set var, 3
+.endif
+# CHECK: .byte 2
+.byte var
Index: test/MC/AsmParser/ifndef.s
===================================================================
--- test/MC/AsmParser/ifndef.s
+++ test/MC/AsmParser/ifndef.s
@@ -27,3 +27,13 @@
 .else
 	.byte 0
 .endif
+
+# .ifndef directive does not count as a use, so ensure redefinition is permitted
+.set var, 1
+.ifndef var
+	.set var, 2
+.else
+	.set var, 3
+.endif
+# CHECK: .byte 3
+.byte var