diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index e6f7c56e77..9b9f3d2b65 100644
--- a/nix/libstore/build.cc
+++ b/nix/libstore/build.cc
@@ -635,7 +635,7 @@ HookInstance::HookInstance()
 HookInstance::~HookInstance()
 {
     try {
-        pid.kill();
+        pid.kill(true);
     } catch (...) {
         ignoreException();
     }
diff --git a/nix/libutil/util.cc b/nix/libutil/util.cc
index b79212018b..22f49f76d5 100644
--- a/nix/libutil/util.cc
+++ b/nix/libutil/util.cc
@@ -740,11 +740,12 @@ Pid::operator pid_t()
 }
 
 
-void Pid::kill()
+void Pid::kill(bool quiet)
 {
     if (pid == -1 || pid == 0) return;
 
-    printMsg(lvlError, format("killing process %1%") % pid);
+    if (!quiet)
+        printMsg(lvlError, format("killing process %1%") % pid);
 
     /* Send the requested signal to the child.  If it has its own
        process group, send the signal to every process in the child
diff --git a/nix/libutil/util.hh b/nix/libutil/util.hh
index cf513c008e..7e538ea033 100644
--- a/nix/libutil/util.hh
+++ b/nix/libutil/util.hh
@@ -253,7 +253,7 @@ public:
     ~Pid();
     void operator =(pid_t pid);
     operator pid_t();
-    void kill();
+    void kill(bool quiet = false);
     int wait(bool block);
     void setSeparatePG(bool separatePG);
     void setKillSignal(int signal);