diff --git a/lib/galaxy/model/custom_types.py b/lib/galaxy/model/custom_types.py
index f36b4b9a6130..762c203eade4 100644
--- a/lib/galaxy/model/custom_types.py
+++ b/lib/galaxy/model/custom_types.py
@@ -32,7 +32,7 @@ class SafeJsonEncoder(json.JSONEncoder):
     def default(self, obj):
         if isinstance(obj, numpy.int_):
             return int(obj)
-        elif isinstance(obj, numpy.float_):
+        elif isinstance(obj, numpy.float64):
             return float(obj)
         elif isinstance(obj, bytes):
             return unicodify(obj)