diff --git a/.github/workflows/linux-ci.yml b/.github/workflows/linux-ci.yml
index d86d794e7..85fefc5d9 100644
--- a/.github/workflows/linux-ci.yml
+++ b/.github/workflows/linux-ci.yml
@@ -9,6 +9,13 @@ jobs:
         os: [ubuntu-latest]
         python_version: ['3.12', '3.11', '3.10', '3.9']
         include:
+          - sklearn_version: '==1.5.0'
+            documentation: 0
+            numpy_version: '>=1.21.1'
+            scipy_version: '>=1.7.0'
+            onnx_version: 'onnx==1.16.0'
+            onnxrt_version: 'onnxruntime==1.18.0'
+            python_version: '3.12'
           - python_version: '3.12'
             documentation: 0
             numpy_version: '>=1.21.1'
diff --git a/.github/workflows/windows-macos-ci.yml b/.github/workflows/windows-macos-ci.yml
index 06e3d3e48..aebb2da31 100644
--- a/.github/workflows/windows-macos-ci.yml
+++ b/.github/workflows/windows-macos-ci.yml
@@ -9,11 +9,17 @@ jobs:
         os: [windows-latest, macos-latest]
         python_version: ['3.11', '3.10', '3.9']
         include:
+          - sklearn_version: '==1.5.0'
+            python_version: '3.11'
+            numpy_version: '>=1.21.1'
+            scipy_version: '>=1.7.0'
+            onnx_version: 'onnx==1.16.0'
+            onnxrt_version: 'onnxruntime==1.18.0'
           - python_version: '3.11'
             numpy_version: '>=1.21.1'
             scipy_version: '>=1.7.0'
             onnx_version: 'onnx<1.16.0'
-            onnxrt_version: 'onnxruntime==1.17.3'
+            onnxrt_version: 'onnxruntime<1.18.0'
             sklearn_version: '==1.3.2'
           - python_version: '3.10'
             numpy_version: '>=1.21.1'
@@ -27,6 +33,12 @@ jobs:
             onnx_version: 'onnx<1.14'
             onnxrt_version: 'onnxruntime<1.16.0'
             sklearn_version: '==1.2.2'
+          - sklearn_version: '==1.4.2'
+            python_version: '3.11'
+            numpy_version: '>=1.21.1'
+            scipy_version: '>=1.7.0'
+            onnx_version: 'onnx>=1.16.0'
+            onnxrt_version: 'onnxruntime>=1.18.0'
 
     steps:
       - name: Checkout repository
diff --git a/skl2onnx/operator_converters/linear_classifier.py b/skl2onnx/operator_converters/linear_classifier.py
index ce8d022e8..d1e20ba3f 100644
--- a/skl2onnx/operator_converters/linear_classifier.py
+++ b/skl2onnx/operator_converters/linear_classifier.py
@@ -60,10 +60,26 @@ def convert_sklearn_linear_classifier(
         intercepts = list(map(lambda x: -1 * x, intercepts)) + intercepts
 
     multi_class = 0
+    use_ovr = False
     if hasattr(op, "multi_class"):
         if op.multi_class == "ovr":
             multi_class = 1
-        else:
+        elif number_of_classes > 2:
+            # See https://scikit-learn.org/dev/modules/generated/
+            # sklearn.linear_model.LogisticRegression.html#sklearn.linear_model.LogisticRegression
+            # multi_class attribute is deprecated.
+            # OVR is not supported anymore.
+            multi_class = 2
+        use_ovr = op.multi_class in ["ovr", "warn"] or (
+            op.multi_class == "auto"
+            and (op.classes_.size <= 2 or op.solver == "liblinear")
+        )
+    else:
+        # See https://scikit-learn.org/dev/modules/generated/
+        # sklearn.linear_model.LogisticRegression.html#sklearn.linear_model.LogisticRegression
+        # multi_class attribute is deprecated.
+        # OVR is not supported anymore.
+        if number_of_classes > 2:
             multi_class = 2
 
     classifier_type = "LinearClassifier"
@@ -77,11 +93,9 @@ def convert_sklearn_linear_classifier(
     ):
         classifier_attrs["post_transform"] = "NONE"
     elif isinstance(op, LogisticRegression):
-        ovr = op.multi_class in ["ovr", "warn"] or (
-            op.multi_class == "auto"
-            and (op.classes_.size <= 2 or op.solver == "liblinear")
+        classifier_attrs["post_transform"] = (
+            "LOGISTIC" if (use_ovr or multi_class == 0) else "SOFTMAX"
         )
-        classifier_attrs["post_transform"] = "LOGISTIC" if ovr else "SOFTMAX"
     else:
         classifier_attrs["post_transform"] = (
             "LOGISTIC" if multi_class > 2 else "SOFTMAX"