diff --git a/sumpy/fmm.py b/sumpy/fmm.py
index 112f75c40b6e64361df027319318f35772aee30b..92a5c2e2fce4b633e918687f219369d95f4d9b65 100644
--- a/sumpy/fmm.py
+++ b/sumpy/fmm.py
@@ -98,7 +98,7 @@ class SumpyExpansionWrangler(object):
         self.tree = tree
         self.dtype = dtype
 
-        if kernel_extra_kwargs is not None:
+        if kernel_extra_kwargs is None:
             kernel_extra_kwargs = {}
 
         self.source_extra_kwargs = source_extra_kwargs