diff --git a/solr/CHANGES.txt b/solr/CHANGES.txt
index 79d18b72f84..85b95218168 100644
--- a/solr/CHANGES.txt
+++ b/solr/CHANGES.txt
@@ -167,6 +167,9 @@ Optimizations
   the "threads" local param on the facet.field param.  This algorithm will
   only be faster in the presence of rapid index changes.  (yonik)
 
+* SOLR-1904: When facet.enum.cache.minDf > 0 and the base doc set is a
+  SortedIntSet, convert to HashDocSet for better performance. (yonik)
+
 Bug Fixes
 ----------------------
 
diff --git a/solr/src/java/org/apache/solr/request/SimpleFacets.java b/solr/src/java/org/apache/solr/request/SimpleFacets.java
index 853a9fa3bfa..235e481c42b 100644
--- a/solr/src/java/org/apache/solr/request/SimpleFacets.java
+++ b/solr/src/java/org/apache/solr/request/SimpleFacets.java
@@ -493,6 +493,14 @@ public class SimpleFacets {
     // Minimum term docFreq in order to use the filterCache for that term.
     int minDfFilterCache = params.getFieldInt(field, FacetParams.FACET_ENUM_CACHE_MINDF, 0);
 
+    // make sure we have a set that is fast for random access, if we will use it for that
+    DocSet fastForRandomSet = docs;
+    if (minDfFilterCache>0 && docs instanceof SortedIntDocSet) {
+      SortedIntDocSet sset = (SortedIntDocSet)docs;
+      fastForRandomSet = new HashDocSet(sset.getDocs(), 0, sset.size());
+    }
+
+
     IndexSchema schema = searcher.getSchema();
     IndexReader r = searcher.getReader();
     FieldType ft = schema.getFieldType(field);
@@ -576,7 +584,7 @@ public class SimpleFacets {
               int[] docArr = bulk.docs.ints;  // this might be movable outside the loop, but perhaps not worth the risk.
               int end = bulk.docs.offset + nDocs;
               for (int i=bulk.docs.offset; i<end; i++) {
-                if (docs.exists(docArr[i])) c++;
+                if (fastForRandomSet.exists(docArr[i])) c++;
               }
             }
           }