diff --git a/preswald/deploy.py b/preswald/deploy.py
index 40ca2c95..cf1322a8 100644
--- a/preswald/deploy.py
+++ b/preswald/deploy.py
@@ -29,6 +29,12 @@ def get_deploy_dir(script_path: str) -> Path:
     return deploy_dir
 
 
+# Google Cloud Run rejects service names of 50 characters or more
+# (`CreateServiceRequest.service_id`), so the generated container name must
+# stay under that limit even after the "preswald-app-" prefix is added.
+GCP_SERVICE_NAME_MAX_LENGTH = 49
+
+
 def get_container_name(script_path: str) -> str:
     """Generate a consistent container name for a given script"""
     script_dir = Path(script_path).parent
@@ -39,6 +45,7 @@ def get_container_name(script_path: str) -> str:
     container_name = container_name.lower()
     container_name = re.sub(r"[^a-z0-9-]", "", container_name)
     container_name = container_name.strip("-")
+    container_name = container_name[:GCP_SERVICE_NAME_MAX_LENGTH].rstrip("-")
     return container_name
 
 
diff --git a/tests/test_deploy.py b/tests/test_deploy.py
new file mode 100644
index 00000000..aabe4b6e
--- /dev/null
+++ b/tests/test_deploy.py
@@ -0,0 +1,41 @@
+import tempfile
+from pathlib import Path
+
+import pytest
+
+from preswald.deploy import GCP_SERVICE_NAME_MAX_LENGTH, get_container_name
+
+
+def _write_toml_project(tmp_path: Path, slug: str) -> Path:
+    script_path = tmp_path / "hello.py"
+    script_path.write_text("")
+    (tmp_path / "preswald.toml").write_text(
+        f'[project]\nslug = "{slug}"\nport = 8501\n'
+    )
+    return script_path
+
+
+def test_get_container_name_stays_under_gcp_limit():
+    # A long-but-valid project slug used to produce a container name past
+    # Cloud Run's <50 char service_id limit once the "preswald-app-" prefix
+    # was added, causing `CreateServiceRequest.service_id` violations (#659).
+    long_slug = "a-very-descriptive-project-slug-for-an-org-1744321134"
+    with tempfile.TemporaryDirectory() as tmp:
+        script_path = _write_toml_project(Path(tmp), long_slug)
+        container_name = get_container_name(str(script_path))
+
+    assert len(container_name) <= GCP_SERVICE_NAME_MAX_LENGTH
+    assert not container_name.endswith("-")
+    assert container_name.startswith("preswald-app-")
+
+
+def test_get_container_name_short_slug_unaffected():
+    with tempfile.TemporaryDirectory() as tmp:
+        script_path = _write_toml_project(Path(tmp), "zwbq")
+        container_name = get_container_name(str(script_path))
+
+    assert container_name == "preswald-app-zwbq"
+
+
+if __name__ == "__main__":
+    raise SystemExit(pytest.main([__file__, "-v"]))