diff --git a/.github/workflows/tests-requirements-old-nopep517.txt b/.github/workflows/tests-requirements-old-nopep517.txt
deleted file mode 100644
index f11dbd0c..00000000
--- a/.github/workflows/tests-requirements-old-nopep517.txt
+++ /dev/null
@@ -1 +0,0 @@
-gvar==11.11
diff --git a/.github/workflows/tests-requirements-old.txt b/.github/workflows/tests-requirements-old.txt
deleted file mode 100644
index fa821470..00000000
--- a/.github/workflows/tests-requirements-old.txt
+++ /dev/null
@@ -1,10 +0,0 @@
-numpy==1.20
-scipy==1.5
-jax==0.4.6
-jaxlib==0.4.6
-pytest
-coverage[toml]
-mpmath
-pandas<1.5
-polars==0.15.16
-pyarrow==10.0.1
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 0474d35b..a56f453f 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -64,10 +64,7 @@ jobs:
         if: matrix.python-version == '3.8'
         run: |
           python -m pip install --upgrade pip
-          python -m pip install -r .github/workflows/tests-requirements-old.txt
-          python -m pip install setuptools wheel # required by --no-use-pep517
-          python -m pip install --no-use-pep517 -r .github/workflows/tests-requirements-old-nopep517.txt
-          python -m pip install .
+          python -m pip install '.[tests-old]'
       - name: Run unit tests
         run: make COVERAGE_SUFFIX=-${{ matrix.os }}-py${{ matrix.python-version }} tests
       - name: Save coverage information
diff --git a/pyproject.toml b/pyproject.toml
index 7c2e9eba..7dbe8239 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -41,9 +41,7 @@ dependencies = [
     'scipy>=1.5', # oldest supported by jax 0.4.6
     'jax>=0.4.6', # first with optimized jnp.vectorize (for BART)
     'jaxlib>=0.4.6',
-    'gvar>=11.10.1,!=11.11.3',
-        # 11.10.1 first supporting gvar.gvar(x, cov) with readonly cov
-        # 11.11.3 gives problems to lsqfit
+    'gvar>=12.0', # 12.0 first with custom formatting
 ]
 dynamic = ["version"]
 
@@ -87,7 +85,7 @@ dev = [ # to work locally on lsqfitgp
 tests = [ # to run the unit tests on CI
     "numpy",
     "scipy",
-    "gvar!=11.11.3",
+    "gvar",
     "jax",
     "jaxlib",
     "pytest",
@@ -97,11 +95,25 @@ tests = [ # to run the unit tests on CI
     "polars[pyarrow]",
 ]
 
+tests-old = [ # to run the unit tests on CI, with minimum supported dependencies
+    "numpy==1.20",
+    "scipy==1.5",
+    "gvar==12.0",
+    "jax==0.4.6",
+    "jaxlib==0.4.6",
+    "pytest",
+    "coverage[toml]",
+    "mpmath",
+    "pandas<1.5",
+    "polars==0.15.16",
+    "pyarrow==10.0.1",
+]
+
 docs = [ # to run examples, documentation code, and build documentation on CI
     "numpy",
     "scipy",
     "matplotlib",
-    "gvar!=11.11.3",
+    "gvar",
     "lsqfit",
     "jax",
     "jaxlib",
diff --git a/src/lsqfitgp/_gvarext/_format.py b/src/lsqfitgp/_gvarext/_format.py
index f8df3a81..3dc4ec95 100644
--- a/src/lsqfitgp/_gvarext/_format.py
+++ b/src/lsqfitgp/_gvarext/_format.py
@@ -275,7 +275,8 @@ def gvar_format(spec=None, *, lsqfitgp_format=True):
     Parameters
     ----------
     spec : str, optional
-        The format specification.
+        The format specification. If not specified and `lsqfitgp_format` is
+        ``True``, use ``'1.5p'``.
     lsqfitgp_format : bool, default True
         Whether to use a modified version of the `gvar` formatting
         specification, provided by `lsqfitgp`.