diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 866964a4c..d4bd650ba 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -79,7 +79,7 @@ typedef std::shared_ptr<Goal> GoalPtr;
 typedef std::weak_ptr<Goal> WeakGoalPtr;
 
 struct CompareGoalPtrs {
-    bool operator() (const GoalPtr & a, const GoalPtr & b);
+    bool operator() (const GoalPtr & a, const GoalPtr & b) const;
 };
 
 /* Set of goals. */
@@ -178,7 +178,7 @@ protected:
 };
 
 
-bool CompareGoalPtrs::operator() (const GoalPtr & a, const GoalPtr & b) {
+bool CompareGoalPtrs::operator() (const GoalPtr & a, const GoalPtr & b) const {
     string s1 = a->key();
     string s2 = b->key();
     return s1 < s2;
diff --git a/src/libutil/logging.cc b/src/libutil/logging.cc
index 011155871..6924e0080 100644
--- a/src/libutil/logging.cc
+++ b/src/libutil/logging.cc
@@ -49,6 +49,7 @@ public:
 
     void startActivity(ActivityId act, Verbosity lvl, ActivityType type,
         const std::string & s, const Fields & fields, ActivityId parent)
+        override
     {
         if (lvl <= verbosity && !s.empty())
             log(lvl, s + "...");
diff --git a/src/nix/command.hh b/src/nix/command.hh
index daa3b3fa7..6b34e3881 100644
--- a/src/nix/command.hh
+++ b/src/nix/command.hh
@@ -6,7 +6,7 @@
 namespace nix {
 
 struct Value;
-struct Bindings;
+class Bindings;
 class EvalState;
 
 /* A command is an argument parser that can be executed by calling its