diff --git a/build/bin/Makefile b/build/bin/Makefile
index d81d9314..c1861871 100644
--- a/build/bin/Makefile
+++ b/build/bin/Makefile
@@ -18,7 +18,7 @@ test-all: prepare-sources
 
 prepare-sources:
 	@ [ -n "`ls /src 2> /dev/null`" ] || (echo "/src doesn't exist or is empty" 1>&2 && exit 1)
-	cp -r /src $(GOPATH)/src/blockbook
+	[ -d $(GOPATH)/src/blockbook ] || cp -r /src $(GOPATH)/src/blockbook
 	$(MAKE) prepare-vendor
 
 prepare-vendor: