diff --git a/src/main/java/org/elasticsearch/cluster/settings/ClusterDynamicSettingsModule.java b/src/main/java/org/elasticsearch/cluster/settings/ClusterDynamicSettingsModule.java
index 4322b209485..200855dfe08 100644
--- a/src/main/java/org/elasticsearch/cluster/settings/ClusterDynamicSettingsModule.java
+++ b/src/main/java/org/elasticsearch/cluster/settings/ClusterDynamicSettingsModule.java
@@ -27,10 +27,10 @@ import org.elasticsearch.cluster.routing.allocation.decider.*;
 import org.elasticsearch.common.inject.AbstractModule;
 import org.elasticsearch.discovery.zen.elect.ElectMasterService;
 import org.elasticsearch.indices.cache.filter.IndicesFilterCache;
+import org.elasticsearch.indices.fielddata.breaker.InternalCircuitBreakerService;
 import org.elasticsearch.indices.recovery.RecoverySettings;
 import org.elasticsearch.indices.store.IndicesStore;
 import org.elasticsearch.indices.ttl.IndicesTTLService;
-import org.elasticsearch.indices.fielddata.breaker.InternalCircuitBreakerService;
 import org.elasticsearch.threadpool.ThreadPool;
 
 /**
@@ -78,7 +78,7 @@ public class ClusterDynamicSettingsModule extends AbstractModule {
         clusterDynamicSettings.addDynamicSetting(DiskThresholdDecider.CLUSTER_ROUTING_ALLOCATION_DISK_THRESHOLD_ENABLED);
         clusterDynamicSettings.addDynamicSetting(InternalClusterInfoService.INTERNAL_CLUSTER_INFO_UPDATE_INTERVAL, Validator.TIME);
         clusterDynamicSettings.addDynamicSetting(SnapshotInProgressAllocationDecider.CLUSTER_ROUTING_ALLOCATION_SNAPSHOT_RELOCATION_ENABLED);
-        clusterDynamicSettings.addDynamicSetting(InternalCircuitBreakerService.CIRCUIT_BREAKER_MAX_BYTES_SETTING, Validator.BYTES_SIZE);
+        clusterDynamicSettings.addDynamicSetting(InternalCircuitBreakerService.CIRCUIT_BREAKER_MAX_BYTES_SETTING, Validator.MEMORY_SIZE);
         clusterDynamicSettings.addDynamicSetting(InternalCircuitBreakerService.CIRCUIT_BREAKER_OVERHEAD_SETTING, Validator.NON_NEGATIVE_DOUBLE);
         clusterDynamicSettings.addDynamicSetting(DestructiveOperations.REQUIRES_NAME);
     }
diff --git a/src/main/java/org/elasticsearch/cluster/settings/Validator.java b/src/main/java/org/elasticsearch/cluster/settings/Validator.java
index b3a2a0842b0..ef37b21352f 100644
--- a/src/main/java/org/elasticsearch/cluster/settings/Validator.java
+++ b/src/main/java/org/elasticsearch/cluster/settings/Validator.java
@@ -24,6 +24,8 @@ import org.elasticsearch.common.Booleans;
 import org.elasticsearch.common.unit.TimeValue;
 
 import static org.elasticsearch.common.unit.ByteSizeValue.parseBytesSizeValue;
+import static org.elasticsearch.common.unit.MemorySizeValue.parseBytesSizeValueOrHeapRatio;
+
 
 /**
  * Validates a setting, returning a failure message if applicable.
@@ -184,7 +186,19 @@ public interface Validator {
             return null;
         }
     };
-    
+
+    public static final Validator MEMORY_SIZE = new Validator() {
+        @Override
+        public String validate(String setting, String value) {
+            try {
+                parseBytesSizeValueOrHeapRatio(value);
+            } catch (ElasticsearchParseException ex) {
+                return ex.getMessage();
+            }
+            return null;
+        }
+    };
+
     public static final Validator BOOLEAN = new Validator() {
         @Override
         public String validate(String setting, String value) {
diff --git a/src/main/java/org/elasticsearch/common/unit/MemorySizeValue.java b/src/main/java/org/elasticsearch/common/unit/MemorySizeValue.java
index 42293b4ed47..81a293459f2 100644
--- a/src/main/java/org/elasticsearch/common/unit/MemorySizeValue.java
+++ b/src/main/java/org/elasticsearch/common/unit/MemorySizeValue.java
@@ -19,6 +19,7 @@
 
 package org.elasticsearch.common.unit;
 
+import org.elasticsearch.ElasticsearchParseException;
 import org.elasticsearch.monitor.jvm.JvmInfo;
 
 import static org.elasticsearch.common.unit.ByteSizeValue.parseBytesSizeValue;
@@ -32,8 +33,16 @@ public enum MemorySizeValue {
      *  the heap is 1G, <tt>10%</tt> will be parsed as <tt>100mb</tt>.  */
     public static ByteSizeValue parseBytesSizeValueOrHeapRatio(String sValue) {
         if (sValue.endsWith("%")) {
-            double percent = Double.parseDouble(sValue.substring(0, sValue.length() - 1));
-            return new ByteSizeValue((long) ((percent / 100) * JvmInfo.jvmInfo().getMem().getHeapMax().bytes()), ByteSizeUnit.BYTES);
+            final String percentAsString = sValue.substring(0, sValue.length() - 1);
+            try {
+                final double percent = Double.parseDouble(percentAsString);
+                if (percent < 0 || percent > 100) {
+                    throw new ElasticsearchParseException("Percentage should be in [0-100], got " + percentAsString);
+                }
+                return new ByteSizeValue((long) ((percent / 100) * JvmInfo.jvmInfo().getMem().getHeapMax().bytes()), ByteSizeUnit.BYTES);
+            } catch (NumberFormatException e) {
+                throw new ElasticsearchParseException("Failed to parse [" + percentAsString + "] as a double", e);
+            }
         } else {
             return parseBytesSizeValue(sValue);
         }
diff --git a/src/main/java/org/elasticsearch/indices/fielddata/breaker/InternalCircuitBreakerService.java b/src/main/java/org/elasticsearch/indices/fielddata/breaker/InternalCircuitBreakerService.java
index 24fe6cb1a1f..c5ac6e5f936 100644
--- a/src/main/java/org/elasticsearch/indices/fielddata/breaker/InternalCircuitBreakerService.java
+++ b/src/main/java/org/elasticsearch/indices/fielddata/breaker/InternalCircuitBreakerService.java
@@ -24,7 +24,6 @@ import org.elasticsearch.common.component.AbstractLifecycleComponent;
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.ByteSizeValue;
-import org.elasticsearch.monitor.jvm.JvmInfo;
 import org.elasticsearch.node.settings.NodeSettingsService;
 
 /**
@@ -39,9 +38,7 @@ public class InternalCircuitBreakerService extends AbstractLifecycleComponent<In
     public static final String CIRCUIT_BREAKER_OVERHEAD_SETTING = "indices.fielddata.breaker.overhead";
 
     public static final double DEFAULT_OVERHEAD_CONSTANT = 1.03;
-
-    private static final long JVM_HEAP_MAX_BYTES = JvmInfo.jvmInfo().getMem().getHeapMax().bytes();
-    private static final long DEFAULT_BREAKER_LIMIT = (long) (0.8 * JVM_HEAP_MAX_BYTES); // 80% of the max heap
+    private static final String DEFAULT_BREAKER_LIMIT = "80%";
 
     private volatile MemoryCircuitBreaker breaker;
     private volatile long maxBytes;
@@ -50,7 +47,7 @@ public class InternalCircuitBreakerService extends AbstractLifecycleComponent<In
     @Inject
     public InternalCircuitBreakerService(Settings settings, NodeSettingsService nodeSettingsService) {
         super(settings);
-        this.maxBytes = settings.getAsBytesSize(CIRCUIT_BREAKER_MAX_BYTES_SETTING, new ByteSizeValue(DEFAULT_BREAKER_LIMIT)).bytes();
+        this.maxBytes = settings.getAsMemory(CIRCUIT_BREAKER_MAX_BYTES_SETTING, DEFAULT_BREAKER_LIMIT).bytes();
         this.overhead = settings.getAsDouble(CIRCUIT_BREAKER_OVERHEAD_SETTING, DEFAULT_OVERHEAD_CONSTANT);
 
         this.breaker = new MemoryCircuitBreaker(new ByteSizeValue(maxBytes), overhead, null, logger);
@@ -62,13 +59,13 @@ public class InternalCircuitBreakerService extends AbstractLifecycleComponent<In
         @Override
         public void onRefreshSettings(Settings settings) {
             // clear breaker now that settings have changed
-            ByteSizeValue newMaxByteSizeValue = settings.getAsBytesSize(CIRCUIT_BREAKER_MAX_BYTES_SETTING, null);
+            long newMaxByteSizeValue = settings.getAsMemory(CIRCUIT_BREAKER_MAX_BYTES_SETTING, DEFAULT_BREAKER_LIMIT).bytes();
             boolean breakerResetNeeded = false;
 
-            if (newMaxByteSizeValue != null) {
+            if (newMaxByteSizeValue != maxBytes) {
                 logger.info("updating [{}] from [{}] to [{}]", CIRCUIT_BREAKER_MAX_BYTES_SETTING,
                         new ByteSizeValue(InternalCircuitBreakerService.this.maxBytes), newMaxByteSizeValue);
-                InternalCircuitBreakerService.this.maxBytes = newMaxByteSizeValue.bytes();
+                maxBytes = newMaxByteSizeValue;
                 breakerResetNeeded = true;
             }
 
@@ -76,7 +73,7 @@ public class InternalCircuitBreakerService extends AbstractLifecycleComponent<In
             if (newOverhead != overhead) {
                 logger.info("updating [{}] from [{}] to [{}]", CIRCUIT_BREAKER_OVERHEAD_SETTING,
                         overhead, newOverhead);
-                InternalCircuitBreakerService.this.overhead = newOverhead;
+                overhead = newOverhead;
                 breakerResetNeeded = true;
             }
 
diff --git a/src/test/java/org/elasticsearch/indices/fielddata/breaker/CircuitBreakerServiceTests.java b/src/test/java/org/elasticsearch/indices/fielddata/breaker/CircuitBreakerServiceTests.java
index f76a1396a66..e1ee896be9f 100644
--- a/src/test/java/org/elasticsearch/indices/fielddata/breaker/CircuitBreakerServiceTests.java
+++ b/src/test/java/org/elasticsearch/indices/fielddata/breaker/CircuitBreakerServiceTests.java
@@ -23,10 +23,13 @@ import org.elasticsearch.action.search.SearchPhaseExecutionException;
 import org.elasticsearch.client.Client;
 import org.elasticsearch.common.collect.MapBuilder;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.monitor.jvm.JvmInfo;
 import org.elasticsearch.test.ElasticsearchIntegrationTest;
 import org.elasticsearch.test.junit.annotations.TestLogging;
 import org.junit.Test;
 
+import java.util.Arrays;
+
 import static org.elasticsearch.common.settings.ImmutableSettings.settingsBuilder;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcked;
 
@@ -36,6 +39,11 @@ import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcke
 @ElasticsearchIntegrationTest.ClusterScope(scope = ElasticsearchIntegrationTest.Scope.TEST)
 public class CircuitBreakerServiceTests extends ElasticsearchIntegrationTest {
 
+    private String randomRidiculouslySmallLimit() {
+        // 3 different ways to say 100 bytes
+        return randomFrom(Arrays.asList("100b", "100", (10000. / JvmInfo.jvmInfo().getMem().getHeapMax().bytes()) + "%"));
+    }
+
     @Test
     @TestLogging("org.elasticsearch.indices.fielddata.breaker:TRACE,org.elasticsearch.index.fielddata:TRACE,org.elasticsearch.common.breaker:TRACE")
     public void testMemoryBreaker() {
@@ -63,7 +71,7 @@ public class CircuitBreakerServiceTests extends ElasticsearchIntegrationTest {
 
             // Update circuit breaker settings
             Settings settings = settingsBuilder()
-                    .put(InternalCircuitBreakerService.CIRCUIT_BREAKER_MAX_BYTES_SETTING, "100b")
+                    .put(InternalCircuitBreakerService.CIRCUIT_BREAKER_MAX_BYTES_SETTING, randomRidiculouslySmallLimit())
                     .put(InternalCircuitBreakerService.CIRCUIT_BREAKER_OVERHEAD_SETTING, 1.05)
                     .build();
             client.admin().cluster().prepareUpdateSettings().setTransientSettings(settings).execute().actionGet();
@@ -120,7 +128,7 @@ public class CircuitBreakerServiceTests extends ElasticsearchIntegrationTest {
 
             // Update circuit breaker settings
             Settings settings = settingsBuilder()
-                    .put(InternalCircuitBreakerService.CIRCUIT_BREAKER_MAX_BYTES_SETTING, "100b")
+                    .put(InternalCircuitBreakerService.CIRCUIT_BREAKER_MAX_BYTES_SETTING, randomRidiculouslySmallLimit())
                     .put(InternalCircuitBreakerService.CIRCUIT_BREAKER_OVERHEAD_SETTING, 1.05)
                     .build();
             client.admin().cluster().prepareUpdateSettings().setTransientSettings(settings).execute().actionGet();