diff --git a/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/InMemoryMetricRepository.java b/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/InMemoryMetricRepository.java
index 1adaf2a8c5..8a62abc539 100644
--- a/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/InMemoryMetricRepository.java
+++ b/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/InMemoryMetricRepository.java
@@ -31,18 +31,26 @@ public class InMemoryMetricRepository implements MetricRepository {
 
 	private ConcurrentMap<String, Measurement> metrics = new ConcurrentHashMap<String, Measurement>();
 
+	private ConcurrentMap<String, Object> locks = new ConcurrentHashMap<String, Object>();
+
 	@Override
 	public void increment(String metricName, int amount, Date timestamp) {
 		Measurement current = this.metrics.get(metricName);
 		if (current != null) {
-			Metric metric = current.getMetric();
-			this.metrics.replace(metricName, current,
-					new Measurement(timestamp, metric.increment(amount)));
-		}
-		else {
-			this.metrics.putIfAbsent(metricName, new Measurement(timestamp, new Metric(
-					metricName, amount)));
+			Object lock = this.locks.putIfAbsent(metricName, new Object());
+			if (lock == null) {
+				lock = this.locks.get(metricName);
+			}
+			synchronized (lock) {
+				current = this.metrics.get(metricName);
+				Metric metric = current.getMetric();
+				this.metrics.replace(metricName, current, new Measurement(timestamp,
+						metric.increment(amount)));
+				return;
+			}
 		}
+		this.metrics.putIfAbsent(metricName, new Measurement(timestamp, new Metric(
+				metricName, amount)));
 	}
 
 	@Override
diff --git a/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/InMemoryMetricRepositoryTests.java b/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/InMemoryMetricRepositoryTests.java
index ad48d2f607..12fa6cb476 100644
--- a/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/InMemoryMetricRepositoryTests.java
+++ b/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/InMemoryMetricRepositoryTests.java
@@ -16,24 +16,65 @@
 
 package org.springframework.boot.actuate.metrics;
 
-import org.junit.Ignore;
-import org.junit.Test;
-import org.springframework.boot.actuate.metrics.InMemoryMetricRepository;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Date;
+import java.util.List;
+import java.util.concurrent.Callable;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
 
-import static org.junit.Assert.fail;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 
 /**
  * Tests for {@link InMemoryMetricRepository}.
  */
-@Ignore
 public class InMemoryMetricRepositoryTests {
 
-	// FIXME write tests
-	// FIXME possibly also add Metric/Measurement tests
+	private InMemoryMetricRepository repository = new InMemoryMetricRepository();
 
 	@Test
-	public void test() {
-		fail("Not yet implemented");
+	public void increment() {
+		this.repository.increment("foo", 1, new Date());
+		assertEquals(1.0, this.repository.findOne("foo").getValue(), 0.01);
+	}
+
+	@Test
+	public void incrementConcurrent() throws Exception {
+		Collection<Callable<Boolean>> tasks = new ArrayList<Callable<Boolean>>();
+		for (int i = 0; i < 100; i++) {
+			tasks.add(new Callable<Boolean>() {
+				@Override
+				public Boolean call() throws Exception {
+					InMemoryMetricRepositoryTests.this.repository.increment("foo", 1,
+							new Date());
+					return true;
+				}
+			});
+			tasks.add(new Callable<Boolean>() {
+				@Override
+				public Boolean call() throws Exception {
+					InMemoryMetricRepositoryTests.this.repository.increment("foo", -1,
+							new Date());
+					return true;
+				}
+			});
+		}
+		List<Future<Boolean>> all = Executors.newFixedThreadPool(10).invokeAll(tasks);
+		for (Future<Boolean> future : all) {
+			assertTrue(future.get(1, TimeUnit.SECONDS));
+		}
+		assertEquals(0, this.repository.findOne("foo").getValue(), 0.01);
+	}
+
+	@Test
+	public void set() {
+		this.repository.set("foo", 1, new Date());
+		assertEquals(1.0, this.repository.findOne("foo").getValue(), 0.01);
 	}
 
 }