diff --git a/Makefile b/Makefile
index 5af46b6..422e133 100644
--- a/Makefile
+++ b/Makefile
@@ -26,6 +26,8 @@ LANGFILTER = $(TMPDIR)/langfilter
 LAANTAS_SCRIPT = $(TMPDIR)/laantas-script
 EXECS = $(LANGFILTER)
 
+CABAL_FLAGS ?= -O
+
 .PHONY: all
 all: build
 
@@ -48,13 +50,13 @@ $(BUILDDIR)/%: %
 	cp $< $@
 
 $(LANGFILTER): langfilter/*.hs langfilter/langfilter.cabal
-	cabal build langfilter
+	cabal build langfilter $(CABAL_FLAGS)
 	mkdir -p $(dir $@)
 	find dist-newstyle -name $(notdir $@) \
 	  -print -type f -exec cp {} $(TMPDIR) \;
 
 $(LAANTAS_SCRIPT): laantas-script/*.hs laantas-script/laantas-script.cabal
-	cabal build laantas-script
+	cabal build laantas-script $(CABAL_FLAGS)
 	mkdir -p $(dir $@)
 	find dist-newstyle -name $(notdir $@) \
 	  -type f -exec cp {} $(TMPDIR) \;