--- a/js/src/ion/TypePolicy.cpp
+++ b/js/src/ion/TypePolicy.cpp
@@ -116,17 +116,19 @@ ComparePolicy::adjustInputs(MInstruction
        compare->setCompareType(MCompare::Compare_Int32);
     }
 
     // Compare_Boolean specialization is done for "Anything === Bool"
     // As of previous line Anything can't be Boolean
     if (compare->compareType() == MCompare::Compare_Boolean) {
         // Unbox rhs that is definitely Boolean
         MDefinition *rhs = def->getOperand(1);
-        if (rhs->type() == MIRType_Value) {
+        if (rhs->type() != MIRType_Boolean) {
+            if (rhs->type() != MIRType_Value)
+                rhs = boxAt(def, rhs);
             MInstruction *unbox = MUnbox::New(rhs, MIRType_Boolean, MUnbox::Infallible);
             def->block()->insertBefore(def, unbox);
             def->replaceOperand(1, unbox);
         }
 
         JS_ASSERT(def->getOperand(0)->type() != MIRType_Boolean);
         JS_ASSERT(def->getOperand(1)->type() == MIRType_Boolean);
         return true;
@@ -140,17 +142,19 @@ ComparePolicy::adjustInputs(MInstruction
        compare->setCompareType(MCompare::Compare_String);
     }
 
     // Compare_StrictString specialization is done for "Anything === String"
     // As of previous line Anything can't be String
     if (compare->compareType() == MCompare::Compare_StrictString) {
         // Unbox rhs that is definitely String
         MDefinition *rhs = def->getOperand(1);
-        if (rhs->type() == MIRType_Value) {
+        if (rhs->type() != MIRType_String) {
+            if (rhs->type() != MIRType_Value)
+                rhs = boxAt(def, rhs);
             MInstruction *unbox = MUnbox::New(rhs, MIRType_String, MUnbox::Infallible);
             def->block()->insertBefore(def, unbox);
             def->replaceOperand(1, unbox);
         }
 
         JS_ASSERT(def->getOperand(0)->type() != MIRType_String);
         JS_ASSERT(def->getOperand(1)->type() == MIRType_String);
         return true;

new file mode 100644
--- /dev/null
+++ b/js/src/jit-test/tests/ion/bug839315.js
@@ -0,0 +1,18 @@
+function f(x) {
+    switch(x) {
+      case 0:
+      case 100:
+    }
+}
+f("");
+evaluate('f({})', { noScriptRval : true });
+
+function g(x) {
+    switch(x) {
+      case 0.1:
+      case 100:
+    }
+}
+
+g(false);
+evaluate('g({})', { noScriptRval : true });