diff --git a/README.md b/README.md
index bdad7f5e..875e291d 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,8 @@ $ cd wireguard-android
 $ ./gradlew assembleRelease
 ```
 
+macOS users may need [flock(1)](https://github.com/discoteq/flock).
+
 ## Embedding
 
 The tunnel library is [on JCenter](https://bintray.com/wireguard/wireguard-android/wireguard-android/_latestVersion), alongside [extensive class library documentation](https://javadoc.io/doc/com.wireguard.android/tunnel).
diff --git a/tunnel/tools/libwg-go/Makefile b/tunnel/tools/libwg-go/Makefile
index 44e7c2be..1a83959a 100644
--- a/tunnel/tools/libwg-go/Makefile
+++ b/tunnel/tools/libwg-go/Makefile
@@ -30,7 +30,7 @@ default: $(DESTDIR)/libwg-go.so
 
 $(GRADLE_USER_HOME)/caches/golang/$(GO_TARBALL):
 	mkdir -p "$(dir $@)"
-	flock -x "$@.lock" -c ' \
+	flock "$@.lock" -c ' \
 	[ -f "$@" ] && exit 0; \
 	curl -o "$@.tmp" "https://dl.google.com/go/$(GO_TARBALL)" && \
 	echo "$(GO_HASH_$(GO_PLATFORM))  $@.tmp" | sha256sum -c && \
@@ -38,7 +38,7 @@ $(GRADLE_USER_HOME)/caches/golang/$(GO_TARBALL):
 
 $(BUILDDIR)/go-$(GO_VERSION)/.prepared: $(GRADLE_USER_HOME)/caches/golang/$(GO_TARBALL)
 	mkdir -p "$(dir $@)"
-	flock -x "$@.lock" -c ' \
+	flock "$@.lock" -c ' \
 	[ -f "$@" ] && exit 0; \
 	tar -C "$(dir $@)" --strip-components=1 -xzf "$^" && \
 	patch -p1 -f -N -r- -d "$(dir $@)" < goruntime-boottime-over-monotonic.diff && \