diff --git a/lib/components/fabro-manifest/src/supplied_workflow.rs b/lib/components/fabro-manifest/src/supplied_workflow.rs
index 9f247294c..0970bf9ff 100644
--- a/lib/components/fabro-manifest/src/supplied_workflow.rs
+++ b/lib/components/fabro-manifest/src/supplied_workflow.rs
@@ -254,6 +254,46 @@ mod tests {
         }
     }
 
+    #[test]
+    fn config_entrypoint_must_be_workflow_toml_beside_its_graph() {
+        let config = "_version = 1\n[workflow]\ngraph = \"g.fabro\"\n[run]\ngoal = \"hello\"\n";
+        let accepted = supplied("sub/workflow.toml", &[
+            ("sub/workflow.toml", config),
+            ("sub/g.fabro", "digraph W {}"),
+        ]);
+        let root = collect(&accepted)
+            .versions()
+            .last()
+            .unwrap()
+            .1
+            .version()
+            .clone();
+        assert!(root.files().contains_key(&root.config_path()));
+
+        // Same tree under another config name: runtime would never read it.
+        let renamed = supplied("sub/run.toml", &[
+            ("sub/run.toml", config),
+            ("sub/g.fabro", "digraph W {}"),
+        ]);
+        let error =
+            collect_supplied_workflow_versions(&renamed.entrypoint, &renamed.files).unwrap_err();
+        assert!(
+            format!("{error:#}").contains("must be `sub/workflow.toml`"),
+            "{error:#}"
+        );
+        // A config that selects a graph in another directory is not its sibling.
+        let elsewhere = supplied("sub/workflow.toml", &[
+            (
+                "sub/workflow.toml",
+                "_version = 1\n[workflow]\ngraph = \"../g.fabro\"\n",
+            ),
+            ("g.fabro", "digraph W {}"),
+        ]);
+        assert!(
+            collect_supplied_workflow_versions(&elsewhere.entrypoint, &elsewhere.files).is_err()
+        );
+    }
+
     #[test]
     fn preserves_literal_scripts_without_executing() {
         let directory = tempfile::tempdir().unwrap();
diff --git a/lib/components/fabro-manifest/src/workflow_bundler.rs b/lib/components/fabro-manifest/src/workflow_bundler.rs
index 9eb0add4a..98202fbe1 100644
--- a/lib/components/fabro-manifest/src/workflow_bundler.rs
+++ b/lib/components/fabro-manifest/src/workflow_bundler.rs
@@ -97,9 +97,22 @@ impl<'a> WorkflowBundler<'a> {
 
         let source = self.read_package_file(&location.graph)?;
         let config = if let Some(workflow_toml_path) = location.toml.as_ref() {
+            let config_path = manifest_path_from_absolute(workflow_toml_path, self.package_root)?;
+            if self.workflow_version_projection {
+                // A version's config is read at run time from the fixed
+                // sibling path only, so a config file under any other name
+                // would be registered and then silently ignored.
+                let expected = dot_path.parent_or_dot().join("workflow.toml");
+                if config_path.as_path() != expected {
+                    bail!(
+                        "workflow configuration `{config_path}` must be `{}` beside its graph \
+                         `{dot_path}`",
+                        expected.display()
+                    );
+                }
+            }
             Some(types::ManifestWorkflowConfig {
-                path:   manifest_path_from_absolute(workflow_toml_path, self.package_root)?
-                    .to_string(),
+                path:   config_path.to_string(),
                 source: self.read_package_file(workflow_toml_path)?,
             })
         } else {