diff --git a/Sources/FrontEnd/TypeChecking/TypeChecker.swift b/Sources/FrontEnd/TypeChecking/TypeChecker.swift
index 2627dc38d..4238c64bf 100644
--- a/Sources/FrontEnd/TypeChecking/TypeChecker.swift
+++ b/Sources/FrontEnd/TypeChecking/TypeChecker.swift
@@ -1355,14 +1355,16 @@ struct TypeChecker {
   }
 
   /// Returns the modules visible as imports in `u`.
+  ///
+  /// The returned set contains the modules declared as explicit imports at the top of `u` along
+  /// with the standard library and the module containing `u`.
   private mutating func imports(exposedTo u: TranslationUnit.ID) -> Set<ModuleDecl.ID> {
     if let result = cache.read(\.imports[u]) {
       return result
     }
 
     // The core library and the containing module are always implicitly imported.
-    var result = Set<ModuleDecl.ID>()
-    result.insert(ModuleDecl.ID(program[u].scope)!)
+    var result: Set<ModuleDecl.ID> = [ModuleDecl.ID(program[u].scope)!]
     if let m = program.ast.coreLibrary {
       result.insert(m)
     }
@@ -2205,7 +2207,7 @@ struct TypeChecker {
 
     // Rule orientation depends on ordering.
     var v = buildTerm(a)
-    var u = b.isTypeParameter ? buildTerm(b) : v.appending(.concrete(b))
+    var u = buildTerm(b)
 
     if let t = TraitDecl.ID(e.decl) {
       v = v.substituting([.parameterType(program[t].receiver)], for: [.trait(t)])
diff --git a/Sources/IR/Emitter.swift b/Sources/IR/Emitter.swift
index 773f5753c..bf6850869 100644
--- a/Sources/IR/Emitter.swift
+++ b/Sources/IR/Emitter.swift
@@ -2516,7 +2516,7 @@ struct Emitter {
   private func unexpectedCoercion(
     from lhs: AnyType, to rhs: AnyType, file: StaticString = #file, line: UInt = #line
   ) -> Never {
-    fatalError("unexpected coercion from '\(lhs)' to \(rhs)", file: file, line: line)
+    fatalError("unexpected coercion from '\(lhs)' to '\(rhs)'", file: file, line: line)
   }
 
   /// Inserts the IR for converting `foreign` to a value of type `ir`.
diff --git a/Tests/HyloTests/TestCases/TypeChecking/ConditionalExtension3.hylo b/Tests/HyloTests/TestCases/TypeChecking/ConditionalExtension3.hylo
new file mode 100644
index 000000000..681e37fe6
--- /dev/null
+++ b/Tests/HyloTests/TestCases/TypeChecking/ConditionalExtension3.hylo
@@ -0,0 +1,20 @@
+//- typeCheck expecting: .failure
+
+type Box<Contents: Regular> {
+  public var contents: Contents
+  public memberwise init
+}
+
+extension Box where Contents == Int {
+  public fun contains_zero() -> Bool {
+    contents == 0
+  }
+}
+
+public fun main() {
+  let b0 = Box(contents: true)
+  _ = b0.contains_zero() //! diagnostic reference to 'contains_zero' requires that 'Bool' be equal to 'Int'
+
+  let b1 = Box(contents: 1)
+  _ = b1.contains_zero()
+}