diff --git a/js/src/jit-test/tests/jaeger/modConstDoubles.js b/js/src/jit-test/tests/jaeger/modConstDoubles.js
new file mode 100644
index 000000000000..807782ce6e4d
--- /dev/null
+++ b/js/src/jit-test/tests/jaeger/modConstDoubles.js
@@ -0,0 +1,8 @@
+
+function f() {
+    var x = 2.6;
+    var y = 2.1;
+    return x % y;
+}
+assertEq(f(), 0.5);
+
diff --git a/js/src/jit-test/tests/jaeger/modConstInt.js b/js/src/jit-test/tests/jaeger/modConstInt.js
new file mode 100644
index 000000000000..cdb0711da3c8
--- /dev/null
+++ b/js/src/jit-test/tests/jaeger/modConstInt.js
@@ -0,0 +1,8 @@
+
+function f() {
+    var i = 1000;
+    var rest = i % 3;
+    var div = (i - rest) / 3;
+    assertEq(div, 333);
+}
+f();
\ No newline at end of file
diff --git a/js/src/jit-test/tests/jaeger/modConstZeroRhs.js b/js/src/jit-test/tests/jaeger/modConstZeroRhs.js
new file mode 100644
index 000000000000..75ef884100bd
--- /dev/null
+++ b/js/src/jit-test/tests/jaeger/modConstZeroRhs.js
@@ -0,0 +1,8 @@
+
+function f() {
+    var x = 5;
+    var y = 0;
+    return x % y;
+}
+assertEq(f(), NaN);
+
diff --git a/js/src/methodjit/FastArithmetic.cpp b/js/src/methodjit/FastArithmetic.cpp
index ff46433e5138..5daba7cab607 100644
--- a/js/src/methodjit/FastArithmetic.cpp
+++ b/js/src/methodjit/FastArithmetic.cpp
@@ -73,10 +73,14 @@ mjit::Compiler::tryBinaryConstantFold(JSContext *cx, FrameState &frame, JSOp op,
       case JSOP_SUB:
       case JSOP_MUL:
       case JSOP_DIV:
-      case JSOP_MOD:
         needInt = false;
         break;
 
+      case JSOP_MOD:
+        needInt = (L.isInt32() && R.isInt32() &&
+                   L.toInt32() >= 0 && R.toInt32() > 0);
+        break;
+
       case JSOP_RSH:
         needInt = true;
         break;
@@ -129,10 +133,12 @@ mjit::Compiler::tryBinaryConstantFold(JSContext *cx, FrameState &frame, JSOp op,
         }
         break;
       case JSOP_MOD:
-        if (dL == 0)
+        if (needInt)
+            nL %= nR;
+        else if (dR == 0)
             dL = js_NaN;
         else
-            dL = js_fmod(dR, dL);
+            dL = js_fmod(dL, dR);
         break;
 
       case JSOP_RSH:
@@ -828,6 +834,10 @@ mjit::Compiler::jsop_mod()
 #if defined(JS_CPU_X86)
     FrameEntry *lhs = frame.peek(-2);
     FrameEntry *rhs = frame.peek(-1);
+
+    if (tryBinaryConstantFold(cx, frame, JSOP_MOD, lhs, rhs))
+        return;
+
     if ((lhs->isTypeKnown() && lhs->getKnownType() != JSVAL_TYPE_INT32) ||
         (rhs->isTypeKnown() && rhs->getKnownType() != JSVAL_TYPE_INT32))
 #endif