--- a/js/xpconnect/src/XPCWrappedNative.cpp
+++ b/js/xpconnect/src/XPCWrappedNative.cpp
@@ -2744,33 +2744,24 @@ CallMethodHelper::ConvertDependentParam(
     } else {
         datum_type = type;
     }
 
     // Specify the correct storage/calling semantics.
     if (paramInfo.IsIndirect())
         dp->SetIndirect();
 
-    // Flag cleanup as necessary for each type.
-    if (isArray) {
-        // Case 1 - Arrays.
-        if (datum_type.IsPointer())
-            dp->SetValNeedsCleanup();
-
-    } else if (isSizedString) {
-        // Case 2 - Sized strings.
+    // We have 3 possible type of dependent parameters: Arrays, Sized Strings,
+    // and iid_is Interface pointers. The latter two always need cleanup, and
+    // arrays need cleanup for all non-arithmetic types. Since the latter two
+    // cases also happen to be non-arithmetic, we can just inspect datum_type
+    // here.
+    if (!datum_type.IsArithmetic())
         dp->SetValNeedsCleanup();
 
-    } else {
-        // Case 3 - Dependent interface pointer.
-        NS_ABORT_IF_FALSE(type.TagPart() == nsXPTType::T_INTERFACE_IS,
-                          "Unknown dependent type.");
-        dp->SetValNeedsCleanup();
-    }
-
     // Even if there's nothing to convert, we still need to examine the
     // JSObject container for out-params. If it's null or otherwise invalid,
     // we want to know before the call, rather than after.
     //
     // This is a no-op for 'in' params.
     jsval src;
     if (!GetOutParamSource(i, &src))
         return JS_FALSE;