diff -Nru apt-cacher-1.7.20/debian/changelog apt-cacher-1.7.20.1/debian/changelog
--- apt-cacher-1.7.20/debian/changelog	2019-01-04 10:45:52.000000000 +0000
+++ apt-cacher-1.7.20.1/debian/changelog	2019-03-24 17:11:53.000000000 +0000
@@ -1,3 +1,10 @@
+apt-cacher (1.7.20.1) unstable; urgency=medium
+
+  * Avoid unnecessary dpkg prompting when upgrading from lenny/squeeze
+    (closes: #905178).
+
+ -- Mark Hindley <mark@hindley.org.uk>  Sun, 24 Mar 2019 17:11:53 +0000
+
 apt-cacher (1.7.20) unstable; urgency=medium
 
   * Add recent Ubuntu release names to commented config file example.
diff -Nru apt-cacher-1.7.20/debian/preinst apt-cacher-1.7.20.1/debian/preinst
--- apt-cacher-1.7.20/debian/preinst	2018-08-31 09:19:24.000000000 +0000
+++ apt-cacher-1.7.20.1/debian/preinst	2019-03-24 17:11:53.000000000 +0000
@@ -22,26 +22,33 @@
 		ucfr --purge apt-cacher $defaultfile 
             fi
 
-	    # Also remove the file itself if it is unmodified to prevent dpkg
-	    # from prompting.
+	    # If ucf kept the squeeze or lenny version of defaultfile, revert
+	    # postinst changes to the AUTOSTART setting to prevent dpkg from
+	    # prompting.
+	    if echo "046661f9e728b783ea90738769219d71 $defaultfile" | md5sum -c >/dev/null 2>&1; then
+		echo "Reverting maintscript changes to squeeze/lenny version of $defaultfile"
+		sed -i s/AUTOSTART=1/AUTOSTART=0/ $defaultfile
+	    else
+		# Remove any unmodified ucf version of defaultfile to prevent dpkg
+		# from prompting.
 
-	    # Test MD5SUMS are:
-	    #  1.7.6: AUTOSTART=0
-	    #  1.7.6: AUTOSTART=1
-	    #  1.7.14: AUTOSTART=0
-	    #  1.7.14: AUTOSTART=1
-	    for test_md5sum in afc7a4b065275465c1eeb5a09c985bde \
-				   f269a1c735ae47d7068db3ba5641a08b \
-				   58440d3f69d8775a54c9c9e482eb90fb \
-				   f7ad90e6cfe327cfab7b16b9206cc56c
-	    do
+		# Test MD5SUMS are:
+		#  1.7.6: AUTOSTART=0
+		#  1.7.6: AUTOSTART=1
+		#  1.7.14: AUTOSTART=0
+		#  1.7.14: AUTOSTART=1
+		for test_md5sum in afc7a4b065275465c1eeb5a09c985bde \
+				       f269a1c735ae47d7068db3ba5641a08b \
+				       58440d3f69d8775a54c9c9e482eb90fb \
+				       f7ad90e6cfe327cfab7b16b9206cc56c
+		do
 		if echo "$test_md5sum $defaultfile" | md5sum -c >/dev/null 2>&1; then
-		    echo "Removing unmodified version of $defaultfile"
+		    echo "Removing unmodified ucf controlled version of $defaultfile"
 		    rm $defaultfile
 		    break
 		fi
-	    done
-
+		done
+	    fi
 	fi ;;
 
     abort-upgrade)