diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 07c5bceb2..2e23dd979 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -3858,7 +3858,7 @@ void DerivationGoal::registerOutputs()
            something like that. */
         canonicalisePathMetaData(actualPath, buildUser ? buildUser->getUID() : -1, inodesSeen);
 
-        debug("scanning for references for output %1 in temp location '%1%'", outputName, actualPath);
+        debug("scanning for references for output '%s' in temp location '%s'", outputName, actualPath);
 
         /* Pass blank Sink as we are not ready to hash data at this stage. */
         NullSink blank;