diff --git a/repos/os/src/app/top/main.cc b/repos/os/src/app/top/main.cc
index 9e990f4ef..9d02f4238 100644
--- a/repos/os/src/app/top/main.cc
+++ b/repos/os/src/app/top/main.cc
@@ -61,7 +61,7 @@ struct Trace_subject_registry
 			return nullptr;
 		}
 
-		enum { MAX_SUBJECTS = 512 };
+		enum { MAX_SUBJECTS = 1024 };
 		Genode::Trace::Subject_id _subjects[MAX_SUBJECTS];
 
 		enum { MAX_CPUS_X = 16, MAX_CPUS_Y = 1, MAX_ELEMENTS_PER_CPU = 6};
@@ -78,6 +78,11 @@ struct Trace_subject_registry
 		{
 			unsigned const num_subjects = trace.subjects(_subjects, MAX_SUBJECTS);
 
+			if (num_subjects == MAX_SUBJECTS)
+				Genode::error("Not enough memory for all threads - "
+				              "calculated utilization is not sane nor "
+				              "complete !", num_subjects);
+
 			/* add and update existing entries */
 			for (unsigned i = 0; i < num_subjects; i++) {