diff --git a/reflex/app.py b/reflex/app.py
index 74ed31fe5..93b5d4d80 100644
--- a/reflex/app.py
+++ b/reflex/app.py
@@ -466,22 +466,29 @@ class App(Base):
         # Compile the pages.
         custom_components = set()
         thread_pool = ThreadPool()
+        compile_results = []
         for route, component in self.pages.items():
             component.add_style(self.style)
-            thread_pool.apply_async(
-                compiler.compile_page,
-                args=(
-                    route,
-                    component,
-                    self.state,
-                    self.connect_error_component,
-                ),
+            compile_results.append(
+                thread_pool.apply_async(
+                    compiler.compile_page,
+                    args=(
+                        route,
+                        component,
+                        self.state,
+                        self.connect_error_component,
+                    ),
+                )
             )
             # Add the custom components from the page to the set.
             custom_components |= component.get_custom_components()
         thread_pool.close()
         thread_pool.join()
 
+        # check the results of all the threads in case an exception was raised.
+        for r in compile_results:
+            r.get()
+
         # Compile the custom components.
         compiler.compile_components(custom_components)
 
diff --git a/reflex/compiler/compiler.py b/reflex/compiler/compiler.py
index 364291efa..bd3c23444 100644
--- a/reflex/compiler/compiler.py
+++ b/reflex/compiler/compiler.py
@@ -78,11 +78,13 @@ def _compile_page(
         state: The app state.
         connect_error_component: The component to render on sever connection error.
 
+
     Returns:
         The compiled component.
     """
     # Merge the default imports with the app-specific imports.
     imports = utils.merge_imports(DEFAULT_IMPORTS, component.get_imports())
+    utils.validate_imports(imports)
     imports = utils.compile_imports(imports)
 
     # Compile the code to render the component.
diff --git a/reflex/compiler/utils.py b/reflex/compiler/utils.py
index 639b0d412..0edba6f78 100644
--- a/reflex/compiler/utils.py
+++ b/reflex/compiler/utils.py
@@ -51,6 +51,28 @@ def compile_import_statement(fields: Set[ImportVar]) -> Tuple[str, Set[str]]:
     return default, rest
 
 
+def validate_imports(imports: imports.ImportDict):
+    """Verify that the same Tag is not used in multiple import.
+
+    Args:
+        imports: The dict of imports to validate
+
+    Raises:
+        ValueError: if a conflict on "tag/alias" is detected for an import.
+    """
+    used_tags = {}
+    for lib, _imports in imports.items():
+        for _import in _imports:
+            import_name = (
+                f"{_import.tag}/{_import.alias}" if _import.alias else _import.tag
+            )
+            if import_name in used_tags:
+                raise ValueError(
+                    f"Can not compile, the tag {import_name} is used multiple time from {lib} and {used_tags[import_name]}"
+                )
+            used_tags[import_name] = lib
+
+
 def compile_imports(imports: imports.ImportDict) -> List[dict]:
     """Compile an import dict.
 
diff --git a/reflex/components/datadisplay/code.py b/reflex/components/datadisplay/code.py
index 4453f75c7..ce736adbe 100644
--- a/reflex/components/datadisplay/code.py
+++ b/reflex/components/datadisplay/code.py
@@ -44,6 +44,8 @@ class CodeBlock(Component):
     # Props passed down to the code tag.
     code_tag_props: Var[Dict[str, str]]
 
+    is_default = True
+
     def _get_imports(self) -> imports.ImportDict:
         merged_imports = super()._get_imports()
         if self.theme is not None: