diff --git a/tools/setup_helpers/cmake.py b/tools/setup_helpers/cmake.py
index dd8f817aba2c2..ed0df72e89847 100644
--- a/tools/setup_helpers/cmake.py
+++ b/tools/setup_helpers/cmake.py
@@ -387,7 +387,7 @@ def build(self, my_env: Dict[str, str]) -> None:
             # then. Until then, we use "--" to pass parameters to the
             # underlying build system.
             build_args += ['--']
-            if IS_WINDOWS:
+            if IS_WINDOWS and not USE_NINJA:
                 # We are likely using msbuild here
                 build_args += ['/p:CL_MPCount={}'.format(max_jobs)]
             else:
diff --git a/tools/test/test_cmake.py b/tools/test/test_cmake.py
index a9fae6dc90e02..ecbce07f52d23 100644
--- a/tools/test/test_cmake.py
+++ b/tools/test/test_cmake.py
@@ -22,7 +22,11 @@ def test_build_jobs(self, mock_cpu_count: unittest.mock.MagicMock) -> None:
             # MAX_JOBS, USE_NINJA, IS_WINDOWS,         want
             ((     '8',      True,     False),          ['-j', '8']),  # noqa: E201,E241
             ((    None,      True,     False),                 None),  # noqa: E201,E241
+            ((     '7',     False,     False),          ['-j', '7']),  # noqa: E201,E241
+            ((    None,     False,     False),         ['-j', '13']),  # noqa: E201,E241
+            ((     '6',      True,      True),          ['-j', '6']),  # noqa: E201,E241
             ((    None,      True,      True),                 None),  # noqa: E201,E241
+            ((    '11',     False,      True), ['/p:CL_MPCount=11']),  # noqa: E201,E241
             ((    None,     False,      True), ['/p:CL_MPCount=13']),  # noqa: E201,E241
         ]
         for (max_jobs, use_ninja, is_windows), want in cases: