diff --git a/pysynphot/spectrum.py b/pysynphot/spectrum.py
index 1b667396..d94a7c25 100644
--- a/pysynphot/spectrum.py
+++ b/pysynphot/spectrum.py
@@ -2083,8 +2083,8 @@ def check_overlap(self, other):
             Overlap status.
 
         """
-        if other.isAnalytic:
-            # then it's defined everywhere
+        if other.isAnalytic and not isinstance(other, Box):
+            # then it's defined everywhere, except for Box
             return 'full'
 
         swave = self.wave[N.where(self.throughput != 0)]