# astropy__astropy-6938
# Loki Mode Multi-Agent Patch
# Attempts: 1

Based on the existing patch and the architect's analysis, here is the fix:

--- a/astropy/io/fits/fitsrec.py
+++ b/astropy/io/fits/fitsrec.py
@@ -1262,7 +1262,7 @@ class FITS_rec(np.recarray):
 
         # Replace exponent separator in floating point numbers
         if 'D' in format:
-            output_field.replace(encode_ascii('E'), encode_ascii('D'))
+            output_field = output_field.replace(encode_ascii('E'), encode_ascii('D'))