diff --git a/.github/workflows/ci_workflows.yml b/.github/workflows/ci_workflows.yml
index 8319921..3056699 100644
--- a/.github/workflows/ci_workflows.yml
+++ b/.github/workflows/ci_workflows.yml
@@ -77,7 +77,7 @@ jobs:
     - name: Set up Python
       uses: actions/setup-python@v4
       with:
-        python-version: '3.10'
+        python-version: '3.11'
     - name: Install and build
       run: |
         python -m pip install --upgrade pip setuptools
@@ -97,10 +97,11 @@ jobs:
     - name: Set up Python
       uses: actions/setup-python@v4
       with:
-        python-version: '3.11'
+        python-version: '3.12-dev'
     - name: Install and build
       run: |
         python -m pip install --upgrade pip setuptools
+        python -m pip install --extra-index-url https://pypi.anaconda.org/scientific-python-nightly-wheels/simple numpy>=0.0.dev0 --pre --upgrade
         python -m pip install --extra-index-url https://pypi.anaconda.org/astropy/simple astropy>=0.0.dev0 --pre --upgrade
         python -m pip install -e .[test]
     - name: Test with dev deps
@@ -143,7 +144,7 @@ jobs:
     - name: Set up Python
       uses: actions/setup-python@v4
       with:
-        python-version: '3.9'
+        python-version: '3.10'
     - name: Install and build
       run: |
         python -m pip install --upgrade pip setuptools
diff --git a/reftools/imphtcomp.py b/reftools/imphtcomp.py
index 0be60d4..10edd7d 100644
--- a/reftools/imphtcomp.py
+++ b/reftools/imphtcomp.py
@@ -291,7 +291,7 @@ def _compare_tables(self):
                         bws2.append(bw2.photbw2[w][flam1.nelem2[i] * j + k])
                         bwdiff.append((bws1[-1] - bws2[-1]) / bws1[-1])
 
-        self.modes = np.array(modes, dtype=np.string_)
+        self.modes = np.array(modes, dtype=np.bytes_)
         self.flams1 = np.array(flams1, dtype=float)
         self.plams1 = np.array(plams1, dtype=float)
         self.bws1 = np.array(bws1, dtype=float)