diff --git a/csharp/ql/integration-tests/posix/conftest.py b/csharp/ql/integration-tests/posix/conftest.py
new file mode 100644
index 000000000000..543bc046c982
--- /dev/null
+++ b/csharp/ql/integration-tests/posix/conftest.py
@@ -0,0 +1,19 @@
+import runs_on
+
+
+def _supports_mono_nuget():
+    """
+    Helper function to determine if the current platform supports Mono and nuget.
+    
+    Returns True if running on Linux or on macOS x86_64 (excluding macos-15 and macos-26).
+    macOS ARM runners (macos-15 and macos-26) are excluded due to issues with Mono and nuget.
+    """
+    return (
+        runs_on.linux
+        or (
+            runs_on.macos
+            and runs_on.x86_64
+            and not runs_on.macos_15
+            and not runs_on.macos_26
+        )
+    )
diff --git a/csharp/ql/integration-tests/posix/standalone_dependencies_no_framework/test.py b/csharp/ql/integration-tests/posix/standalone_dependencies_no_framework/test.py
index d1c1745d69b6..725ded1899c9 100644
--- a/csharp/ql/integration-tests/posix/standalone_dependencies_no_framework/test.py
+++ b/csharp/ql/integration-tests/posix/standalone_dependencies_no_framework/test.py
@@ -1,13 +1,9 @@
-import runs_on
 import pytest
 import os
+from ..conftest import _supports_mono_nuget
 
 
-# Skipping the test on the ARM runners and macos-15, as we're running into trouble with Mono and nuget.
-@pytest.mark.only_if(
-    runs_on.linux
-    or (runs_on.macos and runs_on.x86_64 and not runs_on.macos_15)
-)
+@pytest.mark.only_if(_supports_mono_nuget())
 def test(codeql, csharp):
     os.environ["CODEQL_EXTRACTOR_CSHARP_BUILDLESS_DOTNET_FRAMEWORK_REFERENCES"] = (
         "/non-existent-path"
diff --git a/csharp/ql/integration-tests/posix/standalone_dependencies_nuget with_space/test.py b/csharp/ql/integration-tests/posix/standalone_dependencies_nuget with_space/test.py
index 6d2058c684c2..662178aa3c0f 100644
--- a/csharp/ql/integration-tests/posix/standalone_dependencies_nuget with_space/test.py	
+++ b/csharp/ql/integration-tests/posix/standalone_dependencies_nuget with_space/test.py	
@@ -1,13 +1,9 @@
 import os
-import runs_on
 import pytest
+from ..conftest import _supports_mono_nuget
 
 
-# Skipping the test on the ARM runners and macos-15, as we're running into trouble with Mono and nuget.
-@pytest.mark.only_if(
-    runs_on.linux
-    or (runs_on.macos and runs_on.x86_64 and not runs_on.macos_15)
-)
+@pytest.mark.only_if(_supports_mono_nuget())
 def test(codeql, csharp):
     # making sure we're not doing any fallback restore:
     os.environ["CODEQL_EXTRACTOR_CSHARP_BUILDLESS_NUGET_FEEDS_CHECK_FALLBACK_TIMEOUT"] = "1"
diff --git a/csharp/ql/integration-tests/posix/standalone_dependencies_nuget/test.py b/csharp/ql/integration-tests/posix/standalone_dependencies_nuget/test.py
index 7f88196097ff..d8e8c8055ad5 100644
--- a/csharp/ql/integration-tests/posix/standalone_dependencies_nuget/test.py
+++ b/csharp/ql/integration-tests/posix/standalone_dependencies_nuget/test.py
@@ -1,11 +1,7 @@
-import runs_on
 import pytest
+from ..conftest import _supports_mono_nuget
 
 
-# Skipping the test on the ARM runners and macos-15, as we're running into trouble with Mono and nuget.
-@pytest.mark.only_if(
-    runs_on.linux
-    or (runs_on.macos and runs_on.x86_64 and not runs_on.macos_15)
-)
+@pytest.mark.only_if(_supports_mono_nuget())
 def test(codeql, csharp):
     codeql.database.create(build_mode="none")
diff --git a/csharp/ql/integration-tests/posix/standalone_dependencies_nuget_no_sources/test.py b/csharp/ql/integration-tests/posix/standalone_dependencies_nuget_no_sources/test.py
index 185fb5201f95..ccd8f61a3845 100644
--- a/csharp/ql/integration-tests/posix/standalone_dependencies_nuget_no_sources/test.py
+++ b/csharp/ql/integration-tests/posix/standalone_dependencies_nuget_no_sources/test.py
@@ -1,11 +1,7 @@
-import runs_on
 import pytest
+from ..conftest import _supports_mono_nuget
 
 
-# Skipping the test on the ARM runners, as we're running into trouble with Mono and nuget.
-@pytest.mark.only_if(
-    runs_on.linux
-    or (runs_on.macos and runs_on.x86_64 and not runs_on.macos_15)
-)
+@pytest.mark.only_if(_supports_mono_nuget())
 def test(codeql, csharp):
     codeql.database.create(source_root="proj", build_mode="none")