diff --git a/language-server/src/dotty/tools/languageserver/DottyLanguageServer.scala b/language-server/src/dotty/tools/languageserver/DottyLanguageServer.scala
index de2bc83042d8..b801d3137313 100644
--- a/language-server/src/dotty/tools/languageserver/DottyLanguageServer.scala
+++ b/language-server/src/dotty/tools/languageserver/DottyLanguageServer.scala
@@ -156,7 +156,7 @@ class DottyLanguageServer extends LanguageServer
       val allProjects = drivers.keySet
 
       def transitiveDependencies(config: ProjectConfig): Set[ProjectConfig] = {
-        val dependencies = config.projectDependencies.map(idToConfig).toSet
+        val dependencies = config.projectDependencies.flatMap(idToConfig.get).toSet
         dependencies ++ dependencies.flatMap(transitiveDependencies)
       }