diff --git a/libs/cputimeinstate/cputimeinstate.h b/libs/cputimeinstate/cputimeinstate.h
index 9f6103e..d7b4587 100644
--- a/libs/cputimeinstate/cputimeinstate.h
+++ b/libs/cputimeinstate/cputimeinstate.h
@@ -23,8 +23,9 @@
 namespace bpf {
 
 bool startTrackingUidCpuFreqTimes();
-bool getUidCpuFreqTimes(unsigned int uid, std::vector<std::vector<uint64_t>> *freqTimes);
-bool getUidsCpuFreqTimes(std::unordered_map<uint32_t, std::vector<std::vector<uint64_t>>> *tisMap);
+std::optional<std::vector<std::vector<uint64_t>>> getUidCpuFreqTimes(uint32_t uid);
+std::optional<std::unordered_map<uint32_t, std::vector<std::vector<uint64_t>>>>
+    getUidsCpuFreqTimes();
 bool clearUidCpuFreqTimes(unsigned int uid);
 
 } // namespace bpf