diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 8474ad3..d7a6ce8 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -14,7 +14,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        python-version: [ "3.11", "3.15-dev" ]
+        python-version: [ "3.11", "3.15" ]
         os: [ windows-latest, ubuntu-latest, macos-latest ]
       fail-fast: false
 
@@ -36,6 +36,6 @@ jobs:
 
     - name: Tests
       run: |
-        python -m pytest -s -rxs -v gsw/tests
+        python -m pytest -s -rxs -v -W error gsw/tests
     permissions:
       actions: none
\ No newline at end of file
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 7175202..b738f26 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -20,7 +20,7 @@ repos:
         - --ignore-words-list=nin,preformed,wih,pres,
 
 - repo: https://github.com/tox-dev/pyproject-fmt
-  rev: v2.30.3
+  rev: v2.30.6
   hooks:
     - id: pyproject-fmt
 
@@ -31,7 +31,7 @@ repos:
     - id: ruff
 
 - repo: https://github.com/woodruffw/zizmor-pre-commit
-  rev: v1.31.1
+  rev: v1.32.0
   hooks:
     - id: zizmor
 
diff --git a/gsw/_utilities.py b/gsw/_utilities.py
index f508699..ca1b429 100644
--- a/gsw/_utilities.py
+++ b/gsw/_utilities.py
@@ -51,7 +51,13 @@ def wrapper(*args, **kwargs):
             )
         where = ~mask
 
-        new_kwargs = {"where": where}
+        # Values under the mask are left uninitialized, which is fine for masked
+        # arrays; passing out=None explicitly avoids numpy's "'where' used
+        # without 'out'" warning. Multi-output ufuncs need one None per output.
+        nout = len(f.types[0].split("->")[1]) if hasattr(f, "types") else 1
+        out = None if nout == 1 else (None,) * nout
+
+        new_kwargs = {"where": where, "out": out}
         new_kwargs.update(
             **kwargs
         )  # Allow user override of the where kwarg if they passed it in.
diff --git a/pyproject.toml b/pyproject.toml
index bd7dbbd..5f3577c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -103,3 +103,8 @@ ignore = [
   "tools",
   "tools/*",
 ]
+
+[tool.pytest]
+ini_options.filterwarnings = [
+  "error:::gsw.*",
+]