diff --git a/core/src/main/java/org/elasticsearch/action/admin/indices/mapping/put/PutMappingRequest.java b/core/src/main/java/org/elasticsearch/action/admin/indices/mapping/put/PutMappingRequest.java
index 17fdd6e5f00..7b389dba25a 100644
--- a/core/src/main/java/org/elasticsearch/action/admin/indices/mapping/put/PutMappingRequest.java
+++ b/core/src/main/java/org/elasticsearch/action/admin/indices/mapping/put/PutMappingRequest.java
@@ -35,6 +35,7 @@ import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.index.Index;
 
 import java.io.IOException;
+import java.util.Arrays;
 import java.util.Map;
 import java.util.Objects;
 
@@ -94,8 +95,8 @@ public class PutMappingRequest extends AcknowledgedRequest<PutMappingRequest> im
             validationException = addValidationError("mapping source is empty", validationException);
         }
         if (concreteIndex != null && (indices != null && indices.length > 0)) {
-            validationException = addValidationError("either concreteIndices or unresolved indices can be set concrete: [" + concreteIndex
-                + "] and indices: " + indices , validationException);
+            validationException = addValidationError("either concrete index or unresolved indices can be set, concrete index: ["
+                + concreteIndex + "] and indices: " + Arrays.asList(indices) , validationException);
         }
         return validationException;
     }
diff --git a/core/src/test/java/org/elasticsearch/action/admin/indices/mapping/put/PutMappingRequestTests.java b/core/src/test/java/org/elasticsearch/action/admin/indices/mapping/put/PutMappingRequestTests.java
index 65b9ff0dd22..04892b82339 100644
--- a/core/src/test/java/org/elasticsearch/action/admin/indices/mapping/put/PutMappingRequestTests.java
+++ b/core/src/test/java/org/elasticsearch/action/admin/indices/mapping/put/PutMappingRequestTests.java
@@ -53,6 +53,8 @@ public class PutMappingRequestTests extends ESTestCase {
         r.setConcreteIndex(new Index("foo", "bar"));
         ex = r.validate();
         assertNotNull("source validation should fail", ex);
-        assertTrue(ex.getMessage().contains("either concreteIndices or unresolved indices can be set"));
+        assertEquals(ex.getMessage(),
+            "Validation Failed: 1: either concrete index or unresolved indices can be set," +
+                " concrete index: [[foo/bar]] and indices: [myindex];");
     }
 }
diff --git a/modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ExpressionSearchScript.java b/modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ExpressionSearchScript.java
index 0f56adeea55..3944090cef2 100644
--- a/modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ExpressionSearchScript.java
+++ b/modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ExpressionSearchScript.java
@@ -112,14 +112,16 @@ class ExpressionSearchScript implements SearchScript {
 
             @Override
             public void setNextVar(String name, Object value) {
-                assert(specialValue != null);
                 // this should only be used for the special "_value" variable used in aggregations
                 assert(name.equals("_value"));
 
-                if (value instanceof Number) {
-                    specialValue.setValue(((Number)value).doubleValue());
-                } else {
-                    throw new ScriptException("Cannot use expression with text variable using " + compiledScript);
+                // _value isn't used in script if specialValue == null
+                if (specialValue != null) {
+                    if (value instanceof Number) {
+                        specialValue.setValue(((Number)value).doubleValue());
+                    } else {
+                        throw new ScriptException("Cannot use expression with text variable using " + compiledScript);
+                    }
                 }
             }
         };
diff --git a/modules/lang-expression/src/test/java/org/elasticsearch/script/expression/MoreExpressionTests.java b/modules/lang-expression/src/test/java/org/elasticsearch/script/expression/MoreExpressionTests.java
index 5246d0dc306..a8856ea78b5 100644
--- a/modules/lang-expression/src/test/java/org/elasticsearch/script/expression/MoreExpressionTests.java
+++ b/modules/lang-expression/src/test/java/org/elasticsearch/script/expression/MoreExpressionTests.java
@@ -383,7 +383,11 @@ public class MoreExpressionTests extends ESIntegTestCase {
                                 .script(new Script("_value * 3", ScriptType.INLINE, ExpressionScriptEngineService.NAME, null)))
                 .addAggregation(
                         AggregationBuilders.stats("double_agg").field("y")
-                                .script(new Script("_value - 1.1", ScriptType.INLINE, ExpressionScriptEngineService.NAME, null)));
+                                .script(new Script("_value - 1.1", ScriptType.INLINE, ExpressionScriptEngineService.NAME, null)))
+                .addAggregation(
+                        AggregationBuilders.stats("const_agg").field("x") // specifically to test a script w/o _value
+                                .script(new Script("3.0", ScriptType.INLINE, ExpressionScriptEngineService.NAME, null))
+                );
 
         SearchResponse rsp = req.get();
         assertEquals(3, rsp.getHits().getTotalHits());
@@ -395,6 +399,11 @@ public class MoreExpressionTests extends ESIntegTestCase {
         stats = rsp.getAggregations().get("double_agg");
         assertEquals(0.7, stats.getMax(), 0.0001);
         assertEquals(0.1, stats.getMin(), 0.0001);
+
+        stats = rsp.getAggregations().get("const_agg");
+        assertThat(stats.getMax(), equalTo(3.0));
+        assertThat(stats.getMin(), equalTo(3.0));
+        assertThat(stats.getAvg(), equalTo(3.0));
     }
 
     public void testStringSpecialValueVariable() throws Exception {