diff --git a/pysynphot/spectrum.py b/pysynphot/spectrum.py
index da399e87..a4b3d4d3 100644
--- a/pysynphot/spectrum.py
+++ b/pysynphot/spectrum.py
@@ -2706,7 +2706,7 @@ def __call__(self, wavelength):
         wavelength array as argument.
         """
         if wavelength is None:
-            thru = self.value
+            thru = N.array([self.value], dtype=N.float)
         else:
             thru = N.zeros_like(wavelength, dtype=N.float) + self.value