diff -Nru chezscheme-9.5.4+dfsg/debian/changelog chezscheme-9.5.4+dfsg/debian/changelog
--- chezscheme-9.5.4+dfsg/debian/changelog	2020-09-17 19:27:16.000000000 +0000
+++ chezscheme-9.5.4+dfsg/debian/changelog	2021-04-18 14:54:30.000000000 +0000
@@ -1,3 +1,11 @@
+chezscheme (9.5.4+dfsg-4) unstable; urgency=medium
+
+  * chezscheme.postinst: Clean up obsolete versioned alternatives on
+    upgrades from buster. Thanks to Andreas Beckmann for the report and
+    the patch! (Closes: #986875)
+
+ -- Göran Weinholt <weinholt@debian.org>  Sun, 18 Apr 2021 16:54:30 +0200
+
 chezscheme (9.5.4+dfsg-3) unstable; urgency=medium
 
   * debian/rules: Only override dh_link if chezscheme is built.
diff -Nru chezscheme-9.5.4+dfsg/debian/chezscheme.postinst chezscheme-9.5.4+dfsg/debian/chezscheme.postinst
--- chezscheme-9.5.4+dfsg/debian/chezscheme.postinst	2020-09-07 17:08:14.000000000 +0000
+++ chezscheme-9.5.4+dfsg/debian/chezscheme.postinst	2021-04-18 14:48:44.000000000 +0000
@@ -17,6 +17,13 @@
                         --slave /usr/share/man/man1/scheme-script.1.gz \
                                 scheme-script.1.gz \
                                 /usr/share/man/man1/scheme-script-chez.1.gz
+
+    if dpkg --compare-versions "$2" lt-nl "9.5.4+dfsg-4~" ; then
+        CHEZ_VERSION=9.5
+        update-alternatives --remove scheme /usr/bin/chezscheme${CHEZ_VERSION}
+        update-alternatives --remove scheme-script /usr/bin/chezscheme${CHEZ_VERSION}
+    fi
+
 fi
 
 #DEBHELPER#