diff --git a/flow/Arena.cpp b/flow/Arena.cpp
index dcdaa39ee2..16908dbefd 100644
--- a/flow/Arena.cpp
+++ b/flow/Arena.cpp
@@ -118,14 +118,14 @@ Arena::Arena(Arena&& r) noexcept = default;
 Arena& Arena::operator=(const Arena& r) = default;
 Arena& Arena::operator=(Arena&& r) noexcept = default;
 void Arena::dependsOn(const Arena& p) {
-	if (p.impl) {
+	// x.dependsOn(y) is a no-op if they refer to the same ArenaBlocks.
+	// They will already have the same lifetime.
+	if (p.impl && p.impl.getPtr() != impl.getPtr()) {
 		allowAccess(impl.getPtr());
 		allowAccess(p.impl.getPtr());
 		ArenaBlock::dependOn(impl, p.impl.getPtr());
 		disallowAccess(p.impl.getPtr());
-		if (p.impl.getPtr() != impl.getPtr()) {
-			disallowAccess(impl.getPtr());
-		}
+		disallowAccess(impl.getPtr());
 	}
 }
 
@@ -297,6 +297,7 @@ void* ArenaBlock::make4kAlignedBuffer(uint32_t size) {
 }
 
 void ArenaBlock::dependOn(Reference<ArenaBlock>& self, ArenaBlock* other) {
+	ASSERT(self->getData() != other->getData());
 	other->addref();
 	if (!self || self->isTiny() || self->unused() < sizeof(ArenaBlockRef))
 		create(SMALL, self)->makeReference(other);
@@ -775,6 +776,16 @@ TEST_CASE("/flow/Arena/Size") {
 	return Void();
 }
 
+// Test that x.dependsOn(x) works, and is effectively a no-op.
+TEST_CASE("/flow/Arena/SelfRef") {
+	Arena a(4096);
+
+	// This should be a no-op.
+	a.dependsOn(a);
+
+	return Void();
+}
+
 TEST_CASE("flow/StringRef/eat") {
 	StringRef str = "test/case"_sr;
 	StringRef first = str.eat("/");
@@ -815,4 +826,4 @@ TEST_CASE("flow/StringRef/eat") {
 	ASSERT(str == ""_sr);
 
 	return Void();
-}
\ No newline at end of file
+}