diff --git a/lib/redis/semaphore.rb b/lib/redis/semaphore.rb
index 22e1645..7ab1d77 100644
--- a/lib/redis/semaphore.rb
+++ b/lib/redis/semaphore.rb
@@ -37,7 +37,6 @@ def exists_or_create!
           @redis.set(version_key, API_VERSION)
         end
 
-        set_expiration_if_necessary
         true
       end
     end
@@ -104,6 +103,8 @@ def signal(token = 1)
       @redis.multi do
         @redis.hdel grabbed_key, token
         @redis.lpush available_key, token
+
+        set_expiration_if_necessary
       end
     end
 
diff --git a/spec/semaphore_spec.rb b/spec/semaphore_spec.rb
index 75fdbd3..45f5ff4 100644
--- a/spec/semaphore_spec.rb
+++ b/spec/semaphore_spec.rb
@@ -139,6 +139,15 @@
       sleep 3.0
       expect(@redis.keys.count).to eq(original_key_size)
     end
+
+    it "expires keys after unlocking" do
+      original_key_size = @redis.keys.count
+      semaphore.lock do
+        # noop
+      end
+      sleep 3.0
+      expect(@redis.keys.count).to eq(original_key_size)
+    end
   end
 
   describe "semaphore without staleness checking" do