diff --git a/js/src/ion/shared/Assembler-x86-shared.h b/js/src/ion/shared/Assembler-x86-shared.h
index 75793ccf971..601e251a2b8 100644
--- a/js/src/ion/shared/Assembler-x86-shared.h
+++ b/js/src/ion/shared/Assembler-x86-shared.h
@@ -101,39 +101,33 @@ class AssemblerX86Shared
     };
 
     enum NaNCond {
-        NaN_HandledByCond,
+        NaN_Unexpected,
         NaN_IsTrue,
         NaN_IsFalse
     };
 
-    // If the primary condition returned by ConditionFromDoubleCondition doesn't
-    // handle NaNs properly, return NaN_IsFalse if the comparison should be
-    // overridden to return false on NaN, NaN_IsTrue if it should be overridden
-    // to return true on NaN, or NaN_HandledByCond if no secondary check is
-    // needed.
     static inline NaNCond NaNCondFromDoubleCondition(DoubleCondition cond) {
         switch (cond) {
           case DoubleOrdered:
+          case DoubleEqual:
           case DoubleNotEqual:
           case DoubleGreaterThan:
           case DoubleGreaterThanOrEqual:
           case DoubleLessThan:
           case DoubleLessThanOrEqual:
+            return NaN_IsFalse;
           case DoubleUnordered:
           case DoubleEqualOrUnordered:
+          case DoubleNotEqualOrUnordered:
           case DoubleGreaterThanOrUnordered:
           case DoubleGreaterThanOrEqualOrUnordered:
           case DoubleLessThanOrUnordered:
           case DoubleLessThanOrEqualOrUnordered:
-            return NaN_HandledByCond;
-          case DoubleEqual:
-            return NaN_IsFalse;
-          case DoubleNotEqualOrUnordered:
             return NaN_IsTrue;
         }
 
         JS_NOT_REACHED("Unknown double condition");
-        return NaN_HandledByCond;
+        return NaN_Unexpected;
     }
 
     static void staticAsserts() {
@@ -149,9 +143,6 @@ class AssemblerX86Shared
 
     static Condition InvertCondition(Condition cond);
 
-    // Return the primary condition to test. Some primary conditions may not
-    // handle NaNs properly and may therefore require a secondary condition.
-    // Use NaNCondFromDoubleCondition to determine what else is needed.
     static inline Condition ConditionFromDoubleCondition(DoubleCondition cond) {
         return static_cast<Condition>(cond & ~DoubleConditionBits);
     }
diff --git a/js/src/ion/shared/CodeGenerator-x86-shared.h b/js/src/ion/shared/CodeGenerator-x86-shared.h
index 76916f0c5f2..10727bbfb9c 100644
--- a/js/src/ion/shared/CodeGenerator-x86-shared.h
+++ b/js/src/ion/shared/CodeGenerator-x86-shared.h
@@ -65,7 +65,7 @@ class CodeGeneratorX86Shared : public CodeGeneratorShared
     // Emits a branch that directs control flow to the true block if |cond| is
     // true, and the false block if |cond| is false.
     void emitBranch(Assembler::Condition cond, MBasicBlock *ifTrue, MBasicBlock *ifFalse,
-                    Assembler::NaNCond ifNaN = Assembler::NaN_HandledByCond);
+                    Assembler::NaNCond ifNaN = Assembler::NaN_Unexpected);
     void emitBranch(Assembler::DoubleCondition cond, MBasicBlock *ifTrue, MBasicBlock *ifFalse);
 
     bool emitTableSwitchDispatch(MTableSwitch *mir, const Register &index, const Register &base);
diff --git a/js/src/ion/shared/MacroAssembler-x86-shared.h b/js/src/ion/shared/MacroAssembler-x86-shared.h
index 438c98c9cbf..88ba8c9f4a4 100644
--- a/js/src/ion/shared/MacroAssembler-x86-shared.h
+++ b/js/src/ion/shared/MacroAssembler-x86-shared.h
@@ -423,14 +423,14 @@ class MacroAssemblerX86Shared : public Assembler
     }
 
     void emitSet(Assembler::Condition cond, const Register &dest,
-                 Assembler::NaNCond ifNaN = Assembler::NaN_HandledByCond) {
+                 Assembler::NaNCond ifNaN = Assembler::NaN_Unexpected) {
         if (GeneralRegisterSet(Registers::SingleByteRegs).has(dest)) {
             // If the register we're defining is a single byte register,
             // take advantage of the setCC instruction
             setCC(cond, dest);
             movzxbl(dest, dest);
 
-            if (ifNaN != Assembler::NaN_HandledByCond) {
+            if (ifNaN != Assembler::NaN_Unexpected) {
                 Label noNaN;
                 j(Assembler::NoParity, &noNaN);
                 if (ifNaN == Assembler::NaN_IsTrue)