diff --git a/README.md b/README.md
index 2620f3f..cc1a0d4 100644
--- a/README.md
+++ b/README.md
@@ -74,7 +74,7 @@ Configuration* sibling = LocalProject({ .projectFile = "../Crafter.Math/project.
 cfg.dependencies = { math };
 ```
 
-The sibling's `CrafterBuildProject` gets the args this `project.cpp` was loaded with (`ProjectArgs()`), so `--target=`, `--march=`, `--debug` and the project's own flags reach every sibling down the chain. That is all of them: `cfg.projectArgs` holds only what `ApplyStandardArgs` did not interpret, and passing it on would drop the target and the build type. Set `.args` to send something else: `{}` for nothing, or a list built from the project's args, such as one without a flag only this project reads. Build such a list once and give it to every sibling. A project that two paths load with different lists is built twice, and the program ends up with both builds. Releases up to 2.2.0 forward nothing when `.args` is left out.
+The sibling's `CrafterBuildProject` gets the args this `project.cpp` was loaded with (`ProjectArgs()`), so `--target=`, `--march=`, `--debug` and the project's own flags reach every sibling down the chain. That is all of them: `cfg.projectArgs` holds only what `ApplyStandardArgs` did not interpret, and passing it on would drop the target and the build type. Set `.args` to send something else: `{}` for nothing, or a list built from the project's args, such as one without a flag only this project reads. Build such a list once and give it to every sibling. A project that two paths load with different lists would end up in the program twice, so the build stops with an error that names both paths. Releases up to 2.2.0 forward nothing when `.args` is left out.
 
 The default is read when the spec is made, so make it inside `CrafterBuildProject`, on the thread that calls it. A spec made at namespace scope, on a thread of your own or in a script forwards nothing.
 
diff --git a/interfaces/Crafter.Build-External.cppm b/interfaces/Crafter.Build-External.cppm
index 23ebe6e..327aed1 100644
--- a/interfaces/Crafter.Build-External.cppm
+++ b/interfaces/Crafter.Build-External.cppm
@@ -97,9 +97,9 @@ export namespace Crafter {
     // --debug and the project's own flags reach every sibling down a chain
     // without being passed. Set them to forward something else: {} for
     // nothing, or a list built from this project's args, such as one without
-    // a flag only this project reads. Give such a list to every sibling: a
-    // project that two paths load with two different lists is built twice,
-    // and the program ends up with both builds.
+    // a flag only this project reads. Give such a list to every sibling:
+    // Build() refuses a graph in which two paths load one project with two
+    // different lists, since the program would end up with both builds.
     struct GitProjectSpec {
         GitSource source;
         fs::path projectFile = "project.cpp";