diff --git a/js/src/ion/IonBuilder.cpp b/js/src/ion/IonBuilder.cpp
index 03fbd221912..c5a4dabe1a1 100644
--- a/js/src/ion/IonBuilder.cpp
+++ b/js/src/ion/IonBuilder.cpp
@@ -3060,6 +3060,16 @@ IonBuilder::addTypeBarrier(uint32_t i, CallInfo &callinfo, types::StackTypeSet *
     if (needsBarrier) {
         MTypeBarrier *barrier = MTypeBarrier::New(ins, cloneTypeSet(calleeObs), Bailout_Normal);
         current->add(barrier);
+
+        // Non-matching types are boxed such as the MIRType does not conflict
+        // with the inferred type.
+        if (callerObs->getKnownTypeTag() != calleeObs->getKnownTypeTag() &&
+            ins->type() != MIRType_Value)
+        {
+            MBox *box = MBox::New(ins);
+            current->add(box);
+            ins = box;
+        }
     }
 
     if (i == 0)
diff --git a/js/src/jit-test/tests/ion/bug851067.js b/js/src/jit-test/tests/ion/bug851067.js
new file mode 100644
index 00000000000..79f3b1b1efc
--- /dev/null
+++ b/js/src/jit-test/tests/ion/bug851067.js
@@ -0,0 +1,6 @@
+function toPrinted(value) {
+  value = String(value);
+}
+String = Array;
+toPrinted(123);
+evaluate('toPrinted("foo");');