diff --git a/lib/spack/spack/architecture.py b/lib/spack/spack/architecture.py
index 5341f2dc3b..38ed5baa7b 100644
--- a/lib/spack/spack/architecture.py
+++ b/lib/spack/spack/architecture.py
@@ -356,10 +356,10 @@ def _cmp_key(self):
         return (self.name, self.version)
 
     def to_dict(self):
-        return {
-            'name': self.name,
-            'version': self.version
-        }
+        return syaml_dict([
+            ('name', self.name),
+            ('version', self.version)
+        ])
 
 
 @key_ordering
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 363638c7ea..3bee81c0d4 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -1492,10 +1492,10 @@ def to_node_dict(self, hash=ht.dag_hash):
             d['parameters'] = params
 
         if self.external:
-            d['external'] = {
-                'path': self.external_path,
-                'module': self.external_module
-            }
+            d['external'] = syaml.syaml_dict([
+                ('path', self.external_path),
+                ('module', self.external_module),
+            ])
 
         if not self._concrete:
             d['concrete'] = False
diff --git a/lib/spack/spack/test/spec_yaml.py b/lib/spack/spack/test/spec_yaml.py
index 09440e2622..f9b41df19a 100644
--- a/lib/spack/spack/test/spec_yaml.py
+++ b/lib/spack/spack/test/spec_yaml.py
@@ -8,13 +8,20 @@
 YAML format preserves DAG information in the spec.
 
 """
+import ast
+import inspect
 import os
 
 from collections import Iterable, Mapping
 
+import pytest
+
+import spack.architecture
 import spack.hash_types as ht
+import spack.spec
 import spack.util.spack_json as sjson
 import spack.util.spack_yaml as syaml
+import spack.version
 
 from spack import repo
 from spack.spec import Spec, save_dependency_spec_yamls
@@ -204,6 +211,72 @@ def test_ordered_read_not_required_for_consistent_dag_hash(
         assert spec.full_hash() == round_trip_reversed_json_spec.full_hash()
 
 
+@pytest.mark.parametrize("module", [
+    spack.spec,
+    spack.architecture,
+    spack.version,
+])
+def test_hashes_use_no_python_dicts(module):
+    """Coarse check to make sure we don't use dicts in Spec.to_node_dict().
+
+    Python dicts are not guaranteed to iterate in a deterministic order
+    (at least not in all python versions) so we need to use lists and
+    syaml_dicts.  syaml_dicts are ordered and ensure that hashes in Spack
+    are deterministic.
+
+    This test is intended to handle cases that are not covered by the
+    consistency checks above, or that would be missed by a dynamic check.
+    This test traverses the ASTs of functions that are used in our hash
+    algorithms, finds instances of dictionaries being constructed, and
+    prints out the line numbers where they occur.
+
+    """
+    class FindFunctions(ast.NodeVisitor):
+        """Find a function definition called to_node_dict."""
+        def __init__(self):
+            self.nodes = []
+
+        def visit_FunctionDef(self, node):  # noqa
+            if node.name in ("to_node_dict", "to_dict", "to_dict_or_value"):
+                self.nodes.append(node)
+
+    class FindDicts(ast.NodeVisitor):
+        """Find source locations of dicts in an AST."""
+        def __init__(self, filename):
+            self.nodes = []
+            self.filename = filename
+
+        def add_error(self, node):
+            self.nodes.append(
+                "Use syaml_dict instead of dict at %s:%s:%s"
+                % (self.filename, node.lineno, node.col_offset)
+            )
+
+        def visit_Dict(self, node):  # noqa
+            self.add_error(node)
+
+        def visit_Call(self, node):  # noqa
+            name = None
+            if isinstance(node.func, ast.Name):
+                name = node.func.id
+            elif isinstance(node.func, ast.Attribute):
+                name = node.func.attr
+
+            if name == 'dict':
+                self.add_error(node)
+
+    find_functions = FindFunctions()
+    module_ast = ast.parse(inspect.getsource(module))
+    find_functions.visit(module_ast)
+
+    find_dicts = FindDicts(module.__file__)
+    for node in find_functions.nodes:
+        find_dicts.visit(node)
+
+    # fail with offending lines if we found some dicts.
+    assert [] == find_dicts.nodes
+
+
 def reverse_all_dicts(data):
     """Descend into data and reverse all the dictionaries"""
     if isinstance(data, dict):