diff --git a/heat/engine/resources/stack_resource.py b/heat/engine/resources/stack_resource.py
index f4e4b1131d..576af5e489 100644
--- a/heat/engine/resources/stack_resource.py
+++ b/heat/engine/resources/stack_resource.py
@@ -66,6 +66,8 @@ class StackResource(resource.Resource):
                 self.child_params())
             nested_stack.strict_validate = False
             nested_stack.validate()
+        except AssertionError:
+            raise
         except Exception as ex:
             raise exception.StackValidationFailed(
                 error=_("Failed to validate"),
diff --git a/heat/engine/service.py b/heat/engine/service.py
index cb78aa17ca..a3ac0dce28 100644
--- a/heat/engine/service.py
+++ b/heat/engine/service.py
@@ -556,6 +556,8 @@ class EngineService(service.Service):
     def _validate_new_stack(self, cnxt, stack_name, parsed_template):
         try:
             parsed_template.validate()
+        except AssertionError:
+            raise
         except Exception as ex:
             raise exception.StackValidationFailed(message=six.text_type(ex))
 
diff --git a/heat/engine/stack.py b/heat/engine/stack.py
index 71a5199516..e9d7505a17 100755
--- a/heat/engine/stack.py
+++ b/heat/engine/stack.py
@@ -647,8 +647,10 @@ class Stack(collections.Mapping):
             try:
                 result = res.validate()
             except exception.HeatException as ex:
-                LOG.info(ex)
+                LOG.debug('%s', ex)
                 raise ex
+            except AssertionError:
+                raise
             except Exception as ex:
                 LOG.exception(_LE("Exception: %s"), ex)
                 raise exception.StackValidationFailed(
@@ -674,7 +676,9 @@ class Stack(collections.Mapping):
                     path=[self.t.OUTPUTS],
                     message=message)
             except exception.StackValidationFailed as ex:
-                raise ex
+                raise
+            except AssertionError:
+                raise
             except Exception as ex:
                 raise exception.StackValidationFailed(
                     error='Output validation error',
@@ -1559,6 +1563,8 @@ class Stack(collections.Mapping):
     def resolve_static_data(self, snippet):
         try:
             return self.t.parse(self, snippet)
+        except AssertionError:
+            raise
         except Exception as ex:
             raise exception.StackValidationFailed(
                 message=encodeutils.safe_decode(six.text_type(ex)))