diff --git a/execution.py b/execution.py
index 5f5d6c73834..18005376798 100644
--- a/execution.py
+++ b/execution.py
@@ -384,7 +384,7 @@ def execute(self, prompt, prompt_id, extra_data={}, execute_outputs=[]):
 
 
 
-def validate_inputs(prompt, item, validated):
+def validate_inputs(prompt, item, validated, stack=[]):
     unique_id = item
     if unique_id in validated:
         return validated[unique_id]
@@ -399,6 +399,22 @@ def validate_inputs(prompt, item, validated):
     errors = []
     valid = True
 
+    if unique_id in stack:
+        error = {
+            "type": "infinite_loop",
+            "message": "loop detected in workflow validation",
+            "details": f"detected at {unique_id}",
+            "extra_info": {"stack": f"{stack}"},
+        }
+        errors.append(error)
+        ret = (False, errors, unique_id)
+        validated[unique_id] = ret
+        # don't continue, because we're already here further up the stack
+        return ret
+    
+# add this node to the stack
+    stack.append(unique_id)
+
     for x in required_inputs:
         if x not in inputs:
             error = {
@@ -450,7 +466,7 @@ def validate_inputs(prompt, item, validated):
                 errors.append(error)
                 continue
             try:
-                r = validate_inputs(prompt, o_id, validated)
+                r = validate_inputs(prompt, o_id, validated, stack)
                 if r[0] is False:
                     # `r` will be set in `validated[o_id]` already
                     valid = False
@@ -577,13 +593,18 @@ def validate_inputs(prompt, item, validated):
                         errors.append(error)
                         continue
 
+# pop the node back off the stack:
+    stack.pop()
+
     if len(errors) > 0 or valid is not True:
         ret = (False, errors, unique_id)
     else:
         ret = (True, [], unique_id)
 
-    validated[unique_id] = ret
-    return ret
+# if we had a loop, unique_id will have been marked invalid further down the tree
+    if unique_id not in validated:
+        validated[unique_id] = ret
+    return validated[unique_id]
 
 def full_type_name(klass):
     module = klass.__module__
@@ -615,7 +636,7 @@ def validate_prompt(prompt):
         valid = False
         reasons = []
         try:
-            m = validate_inputs(prompt, o, validated)
+            m = validate_inputs(prompt, o, validated, [])
             valid = m[0]
             reasons = m[1]
         except Exception as ex:
@@ -659,6 +680,8 @@ def validate_prompt(prompt):
                         print(f"* {class_type} {node_id}:")
                         for reason in reasons:
                             print(f"  - {reason['message']}: {reason['details']}")
+                            if 'extra_info' in reason:
+                                print(f"    - {reason['extra_info']}")
                     node_errors[node_id]["dependent_outputs"].append(o)
             print("Output will be ignored")