diff --git a/CHANGES.rst b/CHANGES.rst
index 785c997..1874aff 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,6 +1,8 @@
 1.6.0 (unreleased)
 ==================
 
+- Compatibility with ``astropy`` 7.1. [#403]
+
 1.5.0 (2024-11-19)
 ==================
 
diff --git a/synphot/spectrum.py b/synphot/spectrum.py
index 196649e..e973eec 100644
--- a/synphot/spectrum.py
+++ b/synphot/spectrum.py
@@ -484,7 +484,7 @@ def integrate(self, wavelengths=None, integration_type=None, **kwargs):
                 raise exceptions.SynphotError(
                     'flux_unit cannot be used with unitless spectrum')
             else:
-                self._validate_flux_unit(flux_unit, wav_only=True)
+                flux_unit = self._validate_flux_unit(flux_unit, wav_only=True)
 
         x = self._validate_wavelengths(wavelengths)