diff --git a/update-libstdcxx-prettyprinter.sh b/update-libstdcxx-prettyprinter.sh
index 2e044a1..f508ba1 100755
--- a/update-libstdcxx-prettyprinter.sh
+++ b/update-libstdcxx-prettyprinter.sh
@@ -7,7 +7,7 @@ fi
 
 # Variables to set up for a new GTS update.
 # The latest GTS supported on this branch.
-gts_major=15
+gts_major=16
 # Tests that need to be synced in for this change.  These are required to sync
 # in adjustments to tests due to changes to pretty printer output.
 # Occasionally, a test adjustment may be due to an ABI change, in which case
@@ -32,9 +32,16 @@ branch=`git branch --show-current`
 
 if ! [[ $branch =~ ^c[0-9]+s$ ]]; then echo "Must be run on a valid centos stream branch, not '$branch'"; exit 1; fi
 
-gtsrev=`curl -s https://gitlab.com/redhat/centos-stream/rpms/gcc-toolset-$gts_major-gcc/-/raw/$(git branch --show-current)/gcc-toolset-15-gcc.spec?ref_type=heads | sed -n 's/^%global gitrev //p'`
+gtsrev=`curl -s https://gitlab.com/redhat/centos-stream/rpms/gcc-toolset-$gts_major-gcc/-/raw/$branch/gcc-toolset-$gts_major-gcc.spec?ref_type=heads | sed -n 's/^%global gitrev //p'`
 
-echo "system at $systemrev and GTS at $gtsrev on the vendor branch"
+prev_gts_major=$((gts_major - 1))
+if grep -q "^Patch.*prettyprinter-update-$prev_gts_major" gcc.spec; then
+  baserev=`curl -s https://gitlab.com/redhat/centos-stream/rpms/gcc-toolset-$prev_gts_major-gcc/-/raw/$branch/gcc-toolset-$prev_gts_major-gcc.spec?ref_type=heads | sed -n 's/^%global gitrev //p'`
+  echo "previous GTS $prev_gts_major at $baserev, GTS $gts_major at $gtsrev on the vendor branch"
+else
+  baserev=$systemrev
+  echo "system at $systemrev and GTS $gts_major at $gtsrev on the vendor branch"
+fi
 
 cwd=$PWD
 cleanup() {
@@ -62,14 +69,14 @@ fi
 
 pp_patchfile=gcc$system_major-libstdc++-prettyprinter-update-$gts_major.patch
 tests_patchfile=gcc$system_major-libstdc++-prettyprinter-update-$gts_major-tests.patch
-git fetch -q origin $systemrev $gtsrev
+git fetch -q origin $baserev $gtsrev
 # We limit the update to just the printer, retain the system gcc hook and
 # make-foo.
-git diff --stat --patch $systemrev..$gtsrev -- libstdc++-v3/python/libstdcxx > ../$pp_patchfile
+git diff --stat --patch $baserev..$gtsrev -- libstdc++-v3/python/libstdcxx > ../$pp_patchfile
 echo "Updated $pp_patchfile"
 
 testfiles=$(echo "$tests" | awk '/.+/{printf "libstdc++-v3/testsuite/libstdc++-prettyprinters/%s ", $1}')
-git diff --stat --patch $systemrev..$gtsrev -- $testfiles > ../$tests_patchfile
+git diff --stat --patch $baserev..$gtsrev -- $testfiles > ../$tests_patchfile
 echo "Updated $tests_patchfile"
 
 popd