diff --git a/esmvalcore/_main.py b/esmvalcore/_main.py
index 0488359ffe..96854d8aed 100755
--- a/esmvalcore/_main.py
+++ b/esmvalcore/_main.py
@@ -392,13 +392,28 @@ def run(self,
 
         self._run(recipe, session)
 
+    @staticmethod
+    def _create_session_dir(session):
+        """Create `session.session_dir` or an alternative if it exists."""
+        from .exceptions import RecipeError
+
+        session_dir = session.session_dir
+        for suffix in range(1, 1000):
+            try:
+                session_dir.mkdir(parents=True)
+            except FileExistsError:
+                session_dir = Path(f"{session.session_dir}-{suffix}")
+            else:
+                session.session_name = session_dir.name
+                return
+
+        raise RecipeError(
+            f"Output directory '{session.session_dir}' already exists and"
+            " unable to find alternative, aborting to prevent data loss.")
+
     def _run(self, recipe: Path, session) -> None:
         """Run `recipe` using `session`."""
-        # Create run dir
-        if session.session_dir.exists():
-            print(f"ERROR: output directory {session.session_dir} already"
-                  " exists, aborting to prevent data loss")
-        session.session_dir.mkdir(parents=True)
+        self._create_session_dir(session)
         session.run_dir.mkdir()
 
         # configure logging
diff --git a/tests/unit/main/test_esmvaltool.py b/tests/unit/main/test_esmvaltool.py
index 08a9b15ab4..42aaabc4ec 100644
--- a/tests/unit/main/test_esmvaltool.py
+++ b/tests/unit/main/test_esmvaltool.py
@@ -12,6 +12,7 @@
 import esmvalcore.esgf
 from esmvalcore import __version__
 from esmvalcore._main import HEADER, ESMValTool
+from esmvalcore.exceptions import RecipeError
 
 LOGGER = logging.getLogger(__name__)
 
@@ -134,11 +135,23 @@ def test_run(mocker, session, offline):
     )
 
 
-def test_run_fail_session_dir_exists(session):
+def test_run_session_dir_exists(session):
     program = ESMValTool()
     session.session_dir.mkdir(parents=True)
-    with pytest.raises(FileExistsError):
-        program._run(Path('/path/to/recipe_test.yml'), session)
+    session_dir = session.session_dir
+    program._create_session_dir(session)
+    assert session.session_name == f"{session_dir.name}-1"
+
+
+def test_run_session_dir_exists_alternative_fails(mocker, session):
+    mocker.patch.object(
+        esmvalcore._main.Path,
+        'mkdir',
+        side_effect=FileExistsError,
+    )
+    program = ESMValTool()
+    with pytest.raises(RecipeError):
+        program._create_session_dir(session)
 
 
 def test_clean_preproc_dir(session):