diff --git a/Makefile b/Makefile
index 4dfde82..e59b328 100644
--- a/Makefile
+++ b/Makefile
@@ -118,6 +118,9 @@ all: eval
 
 # Export HERDING_WORLD so that geometry.py picks it up at import time.
 export HERDING_WORLD = $(WORLD)
+# Force Python stdout/stderr unbuffered so progress is visible live when
+# the build is run under tee / nohup / tmux pipes.
+export PYTHONUNBUFFERED = 1
 
 bc_demos: $(BC_DEMOS)
 $(BC_DEMOS):