diff --git a/crates/wasm-pkg-client/src/decoded_component.rs b/crates/wasm-pkg-client/src/decoded_component.rs
index 8c8767d..b6377c1 100644
--- a/crates/wasm-pkg-client/src/decoded_component.rs
+++ b/crates/wasm-pkg-client/src/decoded_component.rs
@@ -208,10 +208,12 @@ fn extract_package_version(decoded: &DecodedWasm) -> Result<(PackageRef, Version
     Ok((package, version))
 }
 
-/// Borrow the inner `wit_parser::Resolve` and resolve a concrete `WorldId`.
-/// For a decoded component the world is fixed; for a WIT package we ask
-/// `Resolve::select_world` to pick one — deferred until needed so a
-/// multi-world WIT package can publish its first version unambiguously.
+/// Borrow the inner `wit_parser::Resolve` and resolve a concrete `WorldId`
+/// for semver checking.
+///
+/// Semver checks compare two versions of the same component, and a
+/// component is defined by exactly one world. Therefore it is considered
+/// an error if a `WitPackage` defines more than one world.
 fn extract_resolve_and_world_id(
     decoded: &DecodedWasm,
 ) -> Result<(&wit_parser::Resolve, wit_parser::WorldId), Error> {
@@ -220,7 +222,7 @@ fn extract_resolve_and_world_id(
         DecodedWasm::WitPackage(resolve, pkg) => {
             let world_id = resolve
                 .select_world(&[*pkg], None)
-                .map_err(Error::InvalidPackage)?;
+                .map_err(|e| Error::InvalidPackage(e.context("we currently do not support multiple wolds, etc...")))?;
             Ok((resolve, world_id))
         }
     }