diff --git a/js/src/ion/MIR.h b/js/src/ion/MIR.h
index 2a25169c5085..fc400485493f 100644
--- a/js/src/ion/MIR.h
+++ b/js/src/ion/MIR.h
@@ -2403,7 +2403,8 @@ class MAdd : public MBinaryArithInstruction
             return false;
         Range *left = getOperand(0)->range();
         Range *right = getOperand(1)->range();
-        return range()->update(Range::add(left, right));
+        Range next = isTruncated() ? Range::addTruncate(left,right) : Range::add(left, right);
+        return range()->update(next);
     }
 };
 
@@ -2445,7 +2446,8 @@ class MSub : public MBinaryArithInstruction
             return false;
         Range *left = getOperand(0)->range();
         Range *right = getOperand(1)->range();
-        return range()->update(Range::sub(left, right));
+        Range next = isTruncated() ? Range::subTruncate(left,right) : Range::sub(left, right);
+        return range()->update(next);
     }
 };
 
diff --git a/js/src/ion/RangeAnalysis.cpp b/js/src/ion/RangeAnalysis.cpp
index 329363c4388d..4ec201b4e75d 100644
--- a/js/src/ion/RangeAnalysis.cpp
+++ b/js/src/ion/RangeAnalysis.cpp
@@ -156,7 +156,7 @@ RangeAnalysis::addBetaNobes()
             if (jsop == JSOP_LT) {
                 smaller = left;
                 greater = right;
-            } else if (JSOP_GT) {
+            } else if (jsop == JSOP_GT) {
                 smaller = right;
                 greater = left;
             }
@@ -321,6 +321,22 @@ Range::sub(const Range *lhs, const Range *rhs)
     return ret;
 
 }
+Range
+Range::addTruncate(const Range *lhs, const Range *rhs)
+{
+    Range ret = Truncate((int64_t)lhs->lower_ + (int64_t)rhs->lower_,
+                         (int64_t)lhs->upper_ + (int64_t)rhs->upper_);
+    return ret;
+}
+
+Range
+Range::subTruncate(const Range *lhs, const Range *rhs)
+{
+    Range ret = Truncate((int64_t)lhs->lower_ - (int64_t)rhs->upper_,
+                         (int64_t)lhs->upper_ - (int64_t)rhs->lower_);
+    return ret;
+}
+
 Range
 Range::and_(const Range *lhs, const Range *rhs)
 {
diff --git a/js/src/ion/RangeAnalysis.h b/js/src/ion/RangeAnalysis.h
index e5162effeec1..8218c4a8c43f 100644
--- a/js/src/ion/RangeAnalysis.h
+++ b/js/src/ion/RangeAnalysis.h
@@ -88,6 +88,14 @@ class Range {
       upper_(other.upper_),
       upper_infinite_(other.upper_infinite_)
     {}
+    static Range Truncate(int64_t l, int64_t h) {
+        Range ret(l,h);
+        if (!ret.isFinite()) {
+            ret.makeLowerInfinite();
+            ret.makeUpperInfinite();
+        }
+        return ret;
+    }
 
     static int64_t abs64(int64_t x) {
 #ifdef WTF_OS_WINDOWS
@@ -110,6 +118,8 @@ class Range {
     void unionWith(const Range *other);
     void unionWith(RangeChangeCount *other);
     static Range intersect(const Range *lhs, const Range *rhs, bool *nullRange);
+    static Range addTruncate(const Range *lhs, const Range *rhs);
+    static Range subTruncate(const Range *lhs, const Range *rhs);
     static Range add(const Range *lhs, const Range *rhs);
     static Range sub(const Range *lhs, const Range *rhs);
     static Range mul(const Range *lhs, const Range *rhs);