diff --git a/c++/src/kj/main.c++ b/c++/src/kj/main.c++
index 4d84294a..d25369f4 100644
--- a/c++/src/kj/main.c++
+++ b/c++/src/kj/main.c++
@@ -631,7 +631,7 @@ void MainBuilder::MainImpl::usageError(StringPtr programName, StringPtr message)

 class MainBuilder::Impl::OptionDisplayOrder {
 public:
-  bool operator()(const Option* a, const Option* b) {
+  bool operator()(const Option* a, const Option* b) const {
     if (a == b) return false;

     char aShort = '\0';
diff --git a/c++/src/kj/time.c++ b/c++/src/kj/time.c++
index 5b3b4334..ead7e4c1 100644
--- a/c++/src/kj/time.c++
+++ b/c++/src/kj/time.c++
@@ -41,7 +41,7 @@ Clock& nullClock() {

 struct TimerImpl::Impl {
   struct TimerBefore {
-    bool operator()(TimerPromiseAdapter* lhs, TimerPromiseAdapter* rhs);
+    bool operator()(TimerPromiseAdapter* lhs, TimerPromiseAdapter* rhs) const;
   };
   using Timers = std::multiset<TimerPromiseAdapter*, TimerBefore>;
   Timers timers;
@@ -75,7 +75,7 @@ private:
 };

 inline bool TimerImpl::Impl::TimerBefore::operator()(
-    TimerPromiseAdapter* lhs, TimerPromiseAdapter* rhs) {
+    TimerPromiseAdapter* lhs, TimerPromiseAdapter* rhs) const {
   return lhs->time < rhs->time;
 }