diff --git a/src/ifcopenshell-python/ifcopenshell/express/rule_compiler.py b/src/ifcopenshell-python/ifcopenshell/express/rule_compiler.py
index 7a39bcb3ac..e844c8d605 100644
--- a/src/ifcopenshell-python/ifcopenshell/express/rule_compiler.py
+++ b/src/ifcopenshell-python/ifcopenshell/express/rule_compiler.py
@@ -444,6 +444,7 @@ def process_expression(context):
 
                 break_points[-1].append(len(args))
 
+                # @todo don't depend on registered schema
                 S = ifcopenshell.ifcopenshell_wrapper.schema_by_name(schema.name)
                 entity = S.declaration_by_name(typename)
                 entity_attributes = entity.attributes()
@@ -806,7 +807,26 @@ if __name__ == "__main__":
     import subprocess
 
     schema = ifcopenshell.express.express_parser.parse(sys.argv[1]).schema
-    ofn = os.path.join(os.path.dirname(__file__), "rules", f"{schema.name}.py")
+    
+    try:
+        ifcopenshell.ifcopenshell_wrapper.schema_by_name(schema.name)
+    except:
+        # @nb note the difference here between:
+        # 
+        #  - ifcopenshell.express.express_parser.parse
+        #  - ifcopenshell.express.parse.parse
+        # 
+        # First generates a pyparsing AST
+        # 
+        # Second populates a latebound schema
+        # that can be registered in C++.
+        builder = ifcopenshell.express.parse(sys.argv[1])
+        ifcopenshell.register_schema(builder)
+
+    try:
+        ofn = sys.argv[2]
+    except IndexError as e:
+        ofn = os.path.join(os.path.dirname(__file__), "rules", f"{schema.name}.py")
     output = io.StringIO()
 
     print("import ifcopenshell", file=output, sep="\n")
@@ -1025,5 +1045,8 @@ INDETERMINATE = indeterminate_type()
     trsf.assign_parent_refs(tree)
     trsf.visit(tree)
 
-    with open(ofn, "w") as f:
-        f.write(ast.unparse(tree))
+    if ofn == "-":
+        print(ast.unparse(tree))
+    else:
+        with open(ofn, "w") as f:
+            f.write(ast.unparse(tree))
diff --git a/src/ifcopenshell-python/ifcopenshell/express/rule_executor.py b/src/ifcopenshell-python/ifcopenshell/express/rule_executor.py
index e73e31707b..0bd9bb5501 100644
--- a/src/ifcopenshell-python/ifcopenshell/express/rule_executor.py
+++ b/src/ifcopenshell-python/ifcopenshell/express/rule_executor.py
@@ -82,7 +82,22 @@ def run(f, logger):
     ifcopenshell.settings.unpack_non_aggregate_inverses = True
 
     fn = os.path.join(os.path.dirname(__file__), "rules", f"{f.schema}.py")
-    source = open(fn, "r").read()
+    try:
+        source = open(fn, "r").read()
+    except FileNotFoundError as e:
+        import sys
+        import time
+        import subprocess
+
+        current_dir_files = {fn.lower(): fn for fn in os.listdir('.')}
+        schema_name = str(f.schema).split(' ')[-1].lower()
+        schema_path = current_dir_files.get(schema_name + '.exp')
+        fn = schema_name + '.py'
+        if not os.path.exists(fn):
+            subprocess.run([sys.executable, "-m", "ifcopenshell.express.rule_compiler", schema_path, fn], check=True)
+            time.sleep(1.)
+        source = open(fn, "r").read()
+
     a = ast.parse(source)
     assertion.rewrite.rewrite_asserts(mod=a, source=source)
     cd = compile(a, f"{f.schema}.py", "exec")