diff --git a/source/dub/project.d b/source/dub/project.d
index 0d2ee19..5b9bcd4 100644
--- a/source/dub/project.d
+++ b/source/dub/project.d
@@ -157,7 +157,7 @@
 				foreach (d; deps) {
 					auto dependency = getDependency(d.name, true);
 					assert(dependency || d.spec.optional,
-						format("Non-optional dependency %s of %s not found in dependency tree!?.", d.name, p.name));
+						format("Non-optional dependency '%s' of '%s' not found in dependency tree!?.", d.name, p.name));
 					if(dependency) perform_rec(dependency);
 					if( ret ) return;
 				}