diff --git a/src/dvsim/flow/base.py b/src/dvsim/flow/base.py
index e90c17d1..e37570d1 100644
--- a/src/dvsim/flow/base.py
+++ b/src/dvsim/flow/base.py
@@ -78,6 +78,7 @@ def __init__(self, flow_cfg_file, hjson_data, args, mk_config) -> None:
         self.project = ""
         self.scratch_path = ""
         self.scratch_base_path = ""
+        self.proj_root = ""
 
         # Add exports using 'exports' keyword - these are exported to the child
         # process' environment.
@@ -154,6 +155,10 @@ def __init__(self, flow_cfg_file, hjson_data, args, mk_config) -> None:
         # _expand and add the code at the start.
         self._expand()
 
+        # Check that proj_root has indeed been defined in the hjson config file
+        if not self.proj_root:
+            raise RuntimeError("Config file did not define proj_root.")
+
         # After initialisation & expansion, save some useful revision metadata
         proj_root = Path(self.proj_root)
         self.commit = git_commit_hash(path=proj_root, short=False)
diff --git a/src/dvsim/job/deploy.py b/src/dvsim/job/deploy.py
index b31f534a..0678a65f 100644
--- a/src/dvsim/job/deploy.py
+++ b/src/dvsim/job/deploy.py
@@ -138,7 +138,7 @@ def get_job_spec(self) -> "JobSpec":
             ),
             workspace_cfg=WorkspaceConfig(
                 timestamp=self.sim_cfg.args.timestamp,
-                project_root=self.sim_cfg.proj_root,
+                project_root=Path(self.sim_cfg.proj_root),
                 scratch_root=Path(self.sim_cfg.scratch_root),
                 scratch_path=Path(self.sim_cfg.scratch_path),
             ),