diff --git a/fuzzers/005-tilegrid/.gitignore b/fuzzers/005-tilegrid/.gitignore
index 65954739..378eac25 100644
--- a/fuzzers/005-tilegrid/.gitignore
+++ b/fuzzers/005-tilegrid/.gitignore
@@ -1,3 +1 @@
-/specimen_*/
-/tilegrid.json
-/run.ok
+build
diff --git a/fuzzers/005-tilegrid/Makefile b/fuzzers/005-tilegrid/Makefile
index c59f83bf..0399ce20 100644
--- a/fuzzers/005-tilegrid/Makefile
+++ b/fuzzers/005-tilegrid/Makefile
@@ -1,17 +1,13 @@
-
-N := 1
-SPECIMENS := $(addprefix specimen_,$(shell seq -f '%03.0f' $(N)))
-SPECIMENS_OK := $(addsuffix /OK,$(SPECIMENS))
-
-database: $(SPECIMENS_OK)
-	cp specimen_001/tilegrid.json tilegrid.json
+database: build/tilegrid.json
 
 pushdb:
-	cp tilegrid.json ${XRAY_DATABASE_DIR}/$(XRAY_DATABASE)/tilegrid.json
+	cp build/tilegrid.json ${XRAY_DATABASE_DIR}/$(XRAY_DATABASE)/tilegrid.json
 
-$(SPECIMENS_OK):
-	bash generate.sh $(subst /OK,,$@)
-	touch $@
+build/tilegrid.json: build/deltas
+	cd build && python3 ../generate.py design_*.delta > tilegrid.json
+
+build/deltas:
+	bash generate.sh build
 
 run:
 	$(MAKE) clean
@@ -20,7 +16,7 @@ run:
 	touch run.ok
 
 clean:
-	rm -rf specimen_[0-9][0-9][0-9]/ tilegrid.json run.ok
+	rm -rf build
 
 .PHONY: database pushdb clean run
 
diff --git a/fuzzers/005-tilegrid/generate.sh b/fuzzers/005-tilegrid/generate.sh
index 3efa2478..a1674bc3 100644
--- a/fuzzers/005-tilegrid/generate.sh
+++ b/fuzzers/005-tilegrid/generate.sh
@@ -11,6 +11,6 @@ done
 for x in design_*.bits; do
 	diff -u design.bits $x | grep '^[-+]bit' > ${x%.bits}.delta
 done
+touch deltas
 
-python3 ../generate.py design_*.delta > tilegrid.json