diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index fa9820087..8af7d5553 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -43,7 +43,7 @@ jobs:
         with:
           tools: tests
 
-      - name: Run coverage (IO tests and Spec tests against PostgreSQL 14)
+      - name: Run coverage (IO tests and Spec tests against PostgreSQL 15)
         run: postgrest-coverage
       - name: Upload coverage to codecov
         uses: codecov/codecov-action@v3.1.1
@@ -63,7 +63,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        pgVersion: [9.6, 10, 11, 12, 13, 14]
+        pgVersion: [9.6, 10, 11, 12, 13, 14, 15]
     name: Test PG ${{ matrix.pgVersion }} (Nix)
     runs-on: ubuntu-latest
     defaults:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 946660726..8bfba2aeb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
  - #2362, Fix error message when [] is used inside select - @wolfgangwalther
  - #2475, Disallow !inner on computed columns - @wolfgangwalther
  - #2285, Ignore leading and trailing spaces in column names when parsing the query string - @wolfgangwalther
+ - #2545, Fix UPSERT with PostgreSQL 15 - @wolfgangwalther
 
 ### Changed
 
diff --git a/default.nix b/default.nix
index 729568cfe..9f4367a9d 100644
--- a/default.nix
+++ b/default.nix
@@ -49,6 +49,7 @@ let
 
   postgresqlVersions =
     [
+      { name = "postgresql-15"; postgresql = pkgs.postgresql_15.withPackages (p: [ p.postgis p.pg_safeupdate ]); }
       { name = "postgresql-14"; postgresql = pkgs.postgresql_14.withPackages (p: [ p.postgis p.pg_safeupdate ]); }
       { name = "postgresql-13"; postgresql = pkgs.postgresql_13.withPackages (p: [ p.postgis p.pg_safeupdate ]); }
       { name = "postgresql-12"; postgresql = pkgs.postgresql_12.withPackages (p: [ p.postgis p.pg_safeupdate ]); }
diff --git a/src/PostgREST/Query/QueryBuilder.hs b/src/PostgREST/Query/QueryBuilder.hs
index 91e54ceff..0cacbdcf6 100644
--- a/src/PostgREST/Query/QueryBuilder.hs
+++ b/src/PostgREST/Query/QueryBuilder.hs
@@ -94,7 +94,7 @@ mutatePlanToQuery (Insert mainQi iCols body onConflct putConditions returnings _
       if null oncCols then
         mempty
       else
-        "ON CONFLICT(" <> BS.intercalate ", " (pgFmtIdent <$> oncCols) <> ") " <> case oncDo of
+        " ON CONFLICT(" <> BS.intercalate ", " (pgFmtIdent <$> oncCols) <> ") " <> case oncDo of
         IgnoreDuplicates ->
           "DO NOTHING"
         MergeDuplicates  ->