diff --git a/src/libstore/build/worker.cc b/src/libstore/build/worker.cc
index 6c96a93bd..f1227a6a1 100644
--- a/src/libstore/build/worker.cc
+++ b/src/libstore/build/worker.cc
@@ -472,4 +472,11 @@ GoalPtr upcast_goal(std::shared_ptr<SubstitutionGoal> subGoal) {
     return subGoal;
 }
 
+void Worker::updateProgress()
+{
+    actDerivations.progress(doneBuilds, expectedBuilds + doneBuilds, runningBuilds, failedBuilds);
+    actSubstitutions.progress(doneSubstitutions, expectedSubstitutions + doneSubstitutions, runningSubstitutions, failedSubstitutions);
+    act.setExpected(actCopyPath, expectedNarSize + doneNarSize);
+}
+
 }
diff --git a/src/libstore/build/worker.hh b/src/libstore/build/worker.hh
index f00cc654b..b6b58d947 100644
--- a/src/libstore/build/worker.hh
+++ b/src/libstore/build/worker.hh
@@ -195,12 +195,7 @@ public:
 
     void markContentsGood(const StorePath & path);
 
-    void updateProgress()
-    {
-        actDerivations.progress(doneBuilds, expectedBuilds + doneBuilds, runningBuilds, failedBuilds);
-        actSubstitutions.progress(doneSubstitutions, expectedSubstitutions + doneSubstitutions, runningSubstitutions, failedSubstitutions);
-        act.setExpected(actCopyPath, expectedNarSize + doneNarSize);
-    }
+    void updateProgress();
 };
 
 }