diff --git a/concore_cli/README.md b/concore_cli/README.md
index e29c7657..b0da5057 100644
--- a/concore_cli/README.md
+++ b/concore_cli/README.md
@@ -79,6 +79,9 @@ Checks:
 - File references and naming conventions
 - ZMQ vs file-based communication
 
+**Options:**
+- `-s, --source <dir>` - Source directory (default: src)
+
 **Example:**
 ```bash
 concore validate workflow.graphml
diff --git a/concore_cli/cli.py b/concore_cli/cli.py
index 6e9ed076..615cb7b9 100644
--- a/concore_cli/cli.py
+++ b/concore_cli/cli.py
@@ -45,10 +45,13 @@ def run(workflow_file, source, output, type, auto_build):
 
 @cli.command()
 @click.argument('workflow_file', type=click.Path(exists=True))
-def validate(workflow_file):
+@click.option('--source', '-s', default='src', help='Source directory')
+def validate(workflow_file, source):
     """Validate a workflow file"""
     try:
-        validate_workflow(workflow_file, console)
+        ok = validate_workflow(workflow_file, source, console)
+        if not ok:
+            sys.exit(1)
     except Exception as e:
         console.print(f"[red]Error:[/red] {str(e)}")
         sys.exit(1)
diff --git a/concore_cli/commands/validate.py b/concore_cli/commands/validate.py
index fa1ea184..74cd7900 100644
--- a/concore_cli/commands/validate.py
+++ b/concore_cli/commands/validate.py
@@ -5,8 +5,9 @@
 import re
 import xml.etree.ElementTree as ET
 
-def validate_workflow(workflow_file, console):
+def validate_workflow(workflow_file, source_dir, console):
     workflow_path = Path(workflow_file)
+    source_root = (workflow_path.parent / source_dir)
     
     console.print(f"[cyan]Validating:[/cyan] {workflow_path.name}")
     console.print()
@@ -15,31 +16,35 @@ def validate_workflow(workflow_file, console):
     warnings = []
     info = []
     
+    def finalize():
+        show_results(console, errors, warnings, info)
+        return len(errors) == 0
+
     try:
         with open(workflow_path, 'r') as f:
             content = f.read()
         
         if not content.strip():
             errors.append("File is empty")
-            return show_results(console, errors, warnings, info)
+            return finalize()
         
         # strict XML syntax check
         try:
             ET.fromstring(content)
         except ET.ParseError as e:
             errors.append(f"Invalid XML: {str(e)}")
-            return show_results(console, errors, warnings, info)
+            return finalize()
         
         try:
             soup = BeautifulSoup(content, 'xml')
         except Exception as e:
             errors.append(f"Invalid XML: {str(e)}")
-            return show_results(console, errors, warnings, info)
+            return finalize()
         
         root = soup.find('graphml')
         if not root:
             errors.append("Not a valid GraphML file - missing <graphml> root element")
-            return show_results(console, errors, warnings, info)
+            return finalize()
             
         # check the graph attributes
         graph = soup.find('graph')
@@ -64,6 +69,9 @@ def validate_workflow(workflow_file, console):
             warnings.append("No edges found in workflow")
         else:
             info.append(f"Found {len(edges)} edge(s)")
+
+        if not source_root.exists():
+            warnings.append(f"Source directory not found: {source_root}")
         
         node_labels = []
         for node in nodes:
@@ -96,6 +104,10 @@ def validate_workflow(workflow_file, console):
                                 errors.append(f"Node '{label}' has no filename")
                             elif not any(filename.endswith(ext) for ext in ['.py', '.cpp', '.m', '.v', '.java']):
                                 warnings.append(f"Node '{label}' has unusual file extension")
+                            elif source_root.exists():
+                                file_path = source_root / filename
+                                if not file_path.exists():
+                                    errors.append(f"Missing source file: {filename}")
                 else:
                     warnings.append(f"Node {node_id} has no label")
             except Exception as e:
@@ -138,12 +150,14 @@ def validate_workflow(workflow_file, console):
         if file_edges > 0:
             info.append(f"File-based edges: {file_edges}")
         
-        show_results(console, errors, warnings, info)
-        
+        return finalize()
+
     except FileNotFoundError:
         console.print(f"[red]Error:[/red] File not found: {workflow_path}")
+        return False
     except Exception as e:
         console.print(f"[red]Validation failed:[/red] {str(e)}")
+        return False
 
 def show_results(console, errors, warnings, info):
     if errors:
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 6aa78109..8d5a3994 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -58,6 +58,19 @@ def test_validate_valid_file(self):
             result = self.runner.invoke(cli, ['validate', 'test-project/workflow.graphml'])
             self.assertEqual(result.exit_code, 0)
             self.assertIn('Validation passed', result.output)
+
+    def test_validate_missing_node_file(self):
+        with self.runner.isolated_filesystem(temp_dir=self.temp_dir):
+            result = self.runner.invoke(cli, ['init', 'test-project'])
+            self.assertEqual(result.exit_code, 0)
+
+            missing_file = Path('test-project/src/script.py')
+            if missing_file.exists():
+                missing_file.unlink()
+
+            result = self.runner.invoke(cli, ['validate', 'test-project/workflow.graphml'])
+            self.assertNotEqual(result.exit_code, 0)
+            self.assertIn('Missing source file', result.output)
     
     def test_status_command(self):
         result = self.runner.invoke(cli, ['status'])