diff --git a/pkg/_macros/CHANGELOG.md b/pkg/_macros/CHANGELOG.md
index e336684afc2e..0b802bc6fb3a 100644
--- a/pkg/_macros/CHANGELOG.md
+++ b/pkg/_macros/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.1.3
+
+- Validate parts in `Code.fromParts()`.
+
 ## 0.1.2
 
 - Add caching for `typeDeclarationOf` results.
diff --git a/pkg/_macros/lib/src/api/code.dart b/pkg/_macros/lib/src/api/code.dart
index 4b7ec6543816..8d2ca664a55f 100644
--- a/pkg/_macros/lib/src/api/code.dart
+++ b/pkg/_macros/lib/src/api/code.dart
@@ -17,9 +17,18 @@ sealed class Code {
 
   Code.fromString(String code) : parts = [code];
 
-  Code.fromParts(this.parts)
-      : assert(parts.every((element) =>
-            element is String || element is Code || element is Identifier));
+  Code.fromParts(this.parts) {
+    for (final part in parts) {
+      switch (part) {
+        case Code():
+        case Identifier():
+        case String():
+          break; // OK
+        default:
+          throw StateError('Unrecognized code part ${part.runtimeType}');
+      }
+    }
+  }
 }
 
 /// An arbitrary chunk of code, which does not have to be syntactically valid
diff --git a/pkg/_macros/pubspec.yaml b/pkg/_macros/pubspec.yaml
index 2badb8ccaeef..661a4523ba8d 100644
--- a/pkg/_macros/pubspec.yaml
+++ b/pkg/_macros/pubspec.yaml
@@ -1,5 +1,5 @@
 name: _macros
-version: 0.1.2
+version: 0.1.3
 description: >-
   This is a private SDK vendored package, which is re-exported by the public
   `macros` package, which is a pub package. Every change to this package is
diff --git a/pkg/front_end/testcases/incremental/macro_change_entry_one.yaml.world.1.expect b/pkg/front_end/testcases/incremental/macro_change_entry_one.yaml.world.1.expect
index 04dcec101301..b5952f23c7e4 100644
--- a/pkg/front_end/testcases/incremental/macro_change_entry_one.yaml.world.1.expect
+++ b/pkg/front_end/testcases/incremental/macro_change_entry_one.yaml.world.1.expect
@@ -49,7 +49,7 @@ holepunch:pkg/_macros/lib/src/api/builders.dart:
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
 holepunch:pkg/_macros/lib/src/api/code.dart:
-- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:460:6)
+- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:469:6)
 - _Enum. (from org-dartlang-sdk:///sdk/lib/core/enum.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
diff --git a/pkg/front_end/testcases/incremental/macro_change_entry_one.yaml.world.2.expect b/pkg/front_end/testcases/incremental/macro_change_entry_one.yaml.world.2.expect
index e05c18459e71..0c95abe7b48c 100644
--- a/pkg/front_end/testcases/incremental/macro_change_entry_one.yaml.world.2.expect
+++ b/pkg/front_end/testcases/incremental/macro_change_entry_one.yaml.world.2.expect
@@ -36,7 +36,7 @@ holepunch:pkg/_macros/lib/src/api/builders.dart:
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
 holepunch:pkg/_macros/lib/src/api/code.dart:
-- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:460:6)
+- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:469:6)
 - _Enum. (from org-dartlang-sdk:///sdk/lib/core/enum.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
diff --git a/pkg/front_end/testcases/incremental/macro_change_entry_two.yaml.world.1.expect b/pkg/front_end/testcases/incremental/macro_change_entry_two.yaml.world.1.expect
index 49a6727ddfe4..371c8d87a291 100644
--- a/pkg/front_end/testcases/incremental/macro_change_entry_two.yaml.world.1.expect
+++ b/pkg/front_end/testcases/incremental/macro_change_entry_two.yaml.world.1.expect
@@ -49,7 +49,7 @@ holepunch:pkg/_macros/lib/src/api/builders.dart:
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
 holepunch:pkg/_macros/lib/src/api/code.dart:
-- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:460:6)
+- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:469:6)
 - _Enum. (from org-dartlang-sdk:///sdk/lib/core/enum.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
diff --git a/pkg/front_end/testcases/incremental/macro_change_entry_two.yaml.world.2.expect b/pkg/front_end/testcases/incremental/macro_change_entry_two.yaml.world.2.expect
index e96d5466b829..0617fd38c4dc 100644
--- a/pkg/front_end/testcases/incremental/macro_change_entry_two.yaml.world.2.expect
+++ b/pkg/front_end/testcases/incremental/macro_change_entry_two.yaml.world.2.expect
@@ -45,7 +45,7 @@ holepunch:pkg/_macros/lib/src/api/builders.dart:
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
 holepunch:pkg/_macros/lib/src/api/code.dart:
-- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:460:6)
+- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:469:6)
 - _Enum. (from org-dartlang-sdk:///sdk/lib/core/enum.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
diff --git a/pkg/front_end/testcases/incremental/macro_change_nestedness.yaml.world.1.expect b/pkg/front_end/testcases/incremental/macro_change_nestedness.yaml.world.1.expect
index f737654d3f98..bd3d21dffef0 100644
--- a/pkg/front_end/testcases/incremental/macro_change_nestedness.yaml.world.1.expect
+++ b/pkg/front_end/testcases/incremental/macro_change_nestedness.yaml.world.1.expect
@@ -69,7 +69,7 @@ holepunch:pkg/_macros/lib/src/api/builders.dart:
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
 holepunch:pkg/_macros/lib/src/api/code.dart:
-- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:460:6)
+- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:469:6)
 - _Enum. (from org-dartlang-sdk:///sdk/lib/core/enum.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
diff --git a/pkg/front_end/testcases/incremental/macro_change_nestedness.yaml.world.2.expect b/pkg/front_end/testcases/incremental/macro_change_nestedness.yaml.world.2.expect
index 811e0c30fc18..c7b0d2e1bdcb 100644
--- a/pkg/front_end/testcases/incremental/macro_change_nestedness.yaml.world.2.expect
+++ b/pkg/front_end/testcases/incremental/macro_change_nestedness.yaml.world.2.expect
@@ -84,7 +84,7 @@ holepunch:pkg/_macros/lib/src/api/builders.dart:
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
 holepunch:pkg/_macros/lib/src/api/code.dart:
-- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:460:6)
+- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:469:6)
 - _Enum. (from org-dartlang-sdk:///sdk/lib/core/enum.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
diff --git a/pkg/front_end/testcases/incremental/macro_recompile.yaml.world.1.expect b/pkg/front_end/testcases/incremental/macro_recompile.yaml.world.1.expect
index f737654d3f98..bd3d21dffef0 100644
--- a/pkg/front_end/testcases/incremental/macro_recompile.yaml.world.1.expect
+++ b/pkg/front_end/testcases/incremental/macro_recompile.yaml.world.1.expect
@@ -69,7 +69,7 @@ holepunch:pkg/_macros/lib/src/api/builders.dart:
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
 holepunch:pkg/_macros/lib/src/api/code.dart:
-- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:460:6)
+- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:469:6)
 - _Enum. (from org-dartlang-sdk:///sdk/lib/core/enum.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
diff --git a/pkg/front_end/testcases/incremental/macro_recompile.yaml.world.2.expect b/pkg/front_end/testcases/incremental/macro_recompile.yaml.world.2.expect
index 7ab638d4a603..a666ddf5b355 100644
--- a/pkg/front_end/testcases/incremental/macro_recompile.yaml.world.2.expect
+++ b/pkg/front_end/testcases/incremental/macro_recompile.yaml.world.2.expect
@@ -66,7 +66,7 @@ holepunch:pkg/_macros/lib/src/api/builders.dart:
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
 holepunch:pkg/_macros/lib/src/api/code.dart:
-- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:460:6)
+- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:469:6)
 - _Enum. (from org-dartlang-sdk:///sdk/lib/core/enum.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
diff --git a/pkg/front_end/testcases/incremental/macro_reuse_compiled_macro.yaml.world.1.expect b/pkg/front_end/testcases/incremental/macro_reuse_compiled_macro.yaml.world.1.expect
index 809fc810edf3..5789a31c8bf0 100644
--- a/pkg/front_end/testcases/incremental/macro_reuse_compiled_macro.yaml.world.1.expect
+++ b/pkg/front_end/testcases/incremental/macro_reuse_compiled_macro.yaml.world.1.expect
@@ -68,7 +68,7 @@ holepunch:pkg/_macros/lib/src/api/builders.dart:
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
 holepunch:pkg/_macros/lib/src/api/code.dart:
-- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:460:6)
+- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:469:6)
 - _Enum. (from org-dartlang-sdk:///sdk/lib/core/enum.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
diff --git a/pkg/front_end/testcases/incremental/macro_reuse_compiled_macro.yaml.world.2.expect b/pkg/front_end/testcases/incremental/macro_reuse_compiled_macro.yaml.world.2.expect
index 70f6a16c976d..325a35a8011d 100644
--- a/pkg/front_end/testcases/incremental/macro_reuse_compiled_macro.yaml.world.2.expect
+++ b/pkg/front_end/testcases/incremental/macro_reuse_compiled_macro.yaml.world.2.expect
@@ -65,7 +65,7 @@ holepunch:pkg/_macros/lib/src/api/builders.dart:
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
 holepunch:pkg/_macros/lib/src/api/code.dart:
-- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:460:6)
+- CodeKind. (from holepunch:pkg/_macros/lib/src/api/code.dart:469:6)
 - _Enum. (from org-dartlang-sdk:///sdk/lib/core/enum.dart)
 - Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart)
 
diff --git a/pkg/macros/CHANGELOG.md b/pkg/macros/CHANGELOG.md
index b73f94ec1291..dbc6a3cf08ac 100644
--- a/pkg/macros/CHANGELOG.md
+++ b/pkg/macros/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.1.0-main.3
+
+- Validate parts in `Code.fromParts()`.
+
 ## 0.1.0-main.2
 
 - Add caching for `typeDeclarationOf` results.
diff --git a/pkg/macros/pubspec.yaml b/pkg/macros/pubspec.yaml
index d804d852974c..a7f087aba713 100644
--- a/pkg/macros/pubspec.yaml
+++ b/pkg/macros/pubspec.yaml
@@ -1,5 +1,5 @@
 name: macros
-version: 0.1.0-main.2
+version: 0.1.0-main.3
 description: >-
   This package is for macro authors, and exposes the APIs necessary to write
   a macro. It exports the APIs from the private `_macros` SDK vendored package.
@@ -11,4 +11,4 @@ environment:
 dependencies:
   _macros:
     sdk: dart
-    version: 0.1.2
+    version: 0.1.3