diff --git a/js/src/jit/IonBuilder.cpp b/js/src/jit/IonBuilder.cpp
index 65f0671f3d3..ab0514821f9 100644
--- a/js/src/jit/IonBuilder.cpp
+++ b/js/src/jit/IonBuilder.cpp
@@ -10146,6 +10146,12 @@ IonBuilder::jsop_in_dense()
     MInitializedLength *initLength = MInitializedLength::New(alloc(), elements);
     current->add(initLength);
 
+    // If there are no holes, speculate the InArray check will not fail.
+    if (!needsHoleCheck && !failedBoundsCheck_) {
+        addBoundsCheck(idInt32, initLength);
+        return pushConstant(BooleanValue(true));
+    }
+
     // Check if id < initLength and elem[id] not a hole.
     MInArray *ins = MInArray::New(alloc(), elements, id, initLength, obj, needsHoleCheck);