diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 1870abead..d59470603 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -590,7 +590,9 @@ HookInstance::HookInstance()
 {
     debug("starting build hook");
 
-    Path buildHook = absPath(getEnv("NIX_BUILD_HOOK"));
+    Path buildHook = getEnv("NIX_BUILD_HOOK");
+    if (string(buildHook, 0, 1) != "/") buildHook = settings.nixLibexecDir + "/nix/" + buildHook;
+    buildHook = canonPath(buildHook);
 
     /* Create a pipe to get the output of the child. */
     fromHook.create();
@@ -1503,7 +1505,7 @@ void DerivationGoal::buildDone()
 
 HookReply DerivationGoal::tryBuildHook()
 {
-    if (!settings.useBuildHook || getEnv("NIX_BUILD_HOOK") == "") return rpDecline;
+    if (!settings.useBuildHook) return rpDecline;
 
     if (!worker.hook)
         worker.hook = std::shared_ptr<HookInstance>(new HookInstance);
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index 8bffdd73f..b9d028be9 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -38,7 +38,7 @@ Settings::Settings()
     thisSystem = SYSTEM;
     maxSilentTime = 0;
     buildTimeout = 0;
-    useBuildHook = true;
+    useBuildHook = getEnv("NIX_BUILD_HOOK") != "";
     printBuildTrace = false;
     reservedSize = 1024 * 1024;
     fsyncMetadata = true;