diff --git a/elementary/messages/block_builders.py b/elementary/messages/block_builders.py
index 31c8d9ba2..dbb6401f9 100644
--- a/elementary/messages/block_builders.py
+++ b/elementary/messages/block_builders.py
@@ -1,5 +1,5 @@
 import json
-from typing import List, Optional, Tuple, Union
+from typing import List, Optional, Sequence, Tuple, Union
 
 from .blocks import (
     CodeBlock,
@@ -16,7 +16,7 @@
 )
 
 SimpleInlineBlock = Union[str, Icon]
-SimpleLineBlock = Union[str, Icon, List[SimpleInlineBlock]]
+SimpleLineBlock = Union[str, Icon, Sequence[SimpleInlineBlock]]
 
 
 def _build_inline_block(
@@ -28,9 +28,9 @@ def _build_inline_block(
 def _build_inlines(
     content: SimpleLineBlock, style: Optional[TextStyle] = None
 ) -> List[InlineBlock]:
-    if isinstance(content, list):
-        return [_build_inline_block(line, style) for line in content]
-    return [_build_inline_block(content)]
+    if isinstance(content, (str, Icon)):
+        return [_build_inline_block(content, style)]
+    return [_build_inline_block(line, style) for line in content]
 
 
 def BulletListBlock(
@@ -73,7 +73,7 @@ def LinkLineBlock(*, text: str, url: str) -> LineBlock:
 
 def SummaryLineBlock(
     *,
-    summary: List[Tuple[SimpleLineBlock, SimpleLineBlock]],
+    summary: Sequence[Tuple[SimpleLineBlock, SimpleLineBlock]],
     include_empty_values: bool = False,
 ) -> LineBlock:
     text_blocks: List[InlineBlock] = []
@@ -89,7 +89,7 @@ def SummaryLineBlock(
 
 def FactsBlock(
     *,
-    facts: List[
+    facts: Sequence[
         Tuple[
             SimpleLineBlock,
             SimpleLineBlock,
diff --git a/elementary/messages/blocks.py b/elementary/messages/blocks.py
index ec0b3201e..a72f5ee4a 100644
--- a/elementary/messages/blocks.py
+++ b/elementary/messages/blocks.py
@@ -2,6 +2,7 @@
 from typing import List, Optional, Union
 
 from pydantic import BaseModel
+from typing_extensions import Literal
 
 
 class Icon(Enum):
@@ -25,6 +26,7 @@ class TextStyle(Enum):
 
 
 class BaseBlock(BaseModel):
+    type: str
     pass
 
 
@@ -33,16 +35,19 @@ class BaseInlineTextBlock(BaseBlock):
 
 
 class TextBlock(BaseInlineTextBlock):
+    type: Literal["text"] = "text"
     text: str
     style: Optional[TextStyle] = None
 
 
 class LinkBlock(BaseInlineTextBlock):
+    type: Literal["link"] = "link"
     text: str
     url: str
 
 
 class IconBlock(BaseInlineTextBlock):
+    type: Literal["icon"] = "icon"
     icon: Icon
 
 
@@ -50,18 +55,21 @@ class IconBlock(BaseInlineTextBlock):
 
 
 class HeaderBlock(BaseBlock):
+    type: Literal["header"] = "header"
     text: str
 
 
 class CodeBlock(BaseBlock):
+    type: Literal["code"] = "code"
     text: str
 
 
 class DividerBlock(BaseBlock):
-    pass
+    type: Literal["divider"] = "divider"
 
 
 class LineBlock(BaseBlock):
+    type: Literal["line"] = "line"
     inlines: List[InlineBlock]
     sep: str = " "
 
@@ -71,19 +79,22 @@ class BaseLinesBlock(BaseBlock):
 
 
 class LinesBlock(BaseLinesBlock):
-    pass
+    type: Literal["lines"] = "lines"
 
 
 class FactBlock(BaseBlock):
+    type: Literal["fact"] = "fact"
     title: LineBlock
     value: LineBlock
 
 
 class FactListBlock(BaseBlock):
+    type: Literal["fact_list"] = "fact_list"
     facts: List[FactBlock]
 
 
 class ExpandableBlock(BaseBlock):
+    type: Literal["expandable"] = "expandable"
     title: str
     body: List["InExpandableBlock"]
     expanded: bool = False
@@ -98,4 +109,5 @@ class ExpandableBlock(BaseBlock):
     "ExpandableBlock",
 ]
 
-ExpandableBlock.model_rebuild()
+# Update forward references for recursive types
+ExpandableBlock.update_forward_refs()
diff --git a/elementary/messages/message_body.py b/elementary/messages/message_body.py
index d2958727a..b41a76208 100644
--- a/elementary/messages/message_body.py
+++ b/elementary/messages/message_body.py
@@ -34,4 +34,4 @@ class MessageBody(BaseModel):
     color: Optional[Color] = None
 
 
-MessageBody.model_rebuild()
+MessageBody.update_forward_refs()