diff --git a/CHANGES.txt b/CHANGES.txt
index 374db56c60..9f4038ff7f 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -3,6 +3,7 @@
  * Add the ability to disable bulk loading of SSTables (CASSANDRA-18781)
  * Clean up obsolete functions and simplify cql_version handling in cqlsh (CASSANDRA-18787)
 Merged from 5.0:
+ * Fix SAI unindexed contexts not considering CONTAINS KEY (CASSANDRA-19040)
  * Ensure that empty SAI column indexes do not fail on validation after full-SSTable streaming (CASSANDRA-19017)
  * SAI in-memory index should check max term size (CASSANDRA-18926)
  * Set default disk_access_mode to mmap_index_only (CASSANDRA-19021)
diff --git a/src/java/org/apache/cassandra/index/sai/plan/QueryController.java b/src/java/org/apache/cassandra/index/sai/plan/QueryController.java
index eee85f016e..b236c61db4 100644
--- a/src/java/org/apache/cassandra/index/sai/plan/QueryController.java
+++ b/src/java/org/apache/cassandra/index/sai/plan/QueryController.java
@@ -146,7 +146,9 @@ public class QueryController
                                                     cfs.getPartitioner(),
                                                     cfs.getComparator(),
                                                     expression.column(),
-                                                    IndexTarget.Type.VALUES,
+                                                    expression.operator().isContainsKey()
+                                                            ? IndexTarget.Type.KEYS
+                                                            : IndexTarget.Type.VALUES,
                                                     null)
                                  : indexes.iterator().next().getIndexContext();
     }
diff --git a/test/unit/org/apache/cassandra/index/sai/cql/CollectionIndexingTest.java b/test/unit/org/apache/cassandra/index/sai/cql/CollectionIndexingTest.java
index a82f539842..b490dfa946 100644
--- a/test/unit/org/apache/cassandra/index/sai/cql/CollectionIndexingTest.java
+++ b/test/unit/org/apache/cassandra/index/sai/cql/CollectionIndexingTest.java
@@ -42,28 +42,28 @@ public class CollectionIndexingTest extends SAITester
     }
 
     @Test
-    public void indexMap() throws Throwable
+    public void indexMap()
     {
         createPopulatedMap(createIndexDDL("value"));
         assertEquals(2, execute("SELECT * FROM %s WHERE value CONTAINS 'v1'").size());
     }
 
     @Test
-    public void indexMapKeys() throws Throwable
+    public void indexMapKeys()
     {
         createPopulatedMap(createIndexDDL("KEYS(value)"));
         assertEquals(2, execute("SELECT * FROM %s WHERE value CONTAINS KEY 1").size());
     }
 
     @Test
-    public void indexMapValues() throws Throwable
+    public void indexMapValues()
     {
         createPopulatedMap(createIndexDDL("VALUES(value)"));
         assertEquals(2, execute("SELECT * FROM %s WHERE value CONTAINS 'v1'").size());
     }
 
     @Test
-    public void indexMapEntries() throws Throwable
+    public void indexMapEntries()
     {
         createPopulatedMap(createIndexDDL("ENTRIES(value)"));
         assertEquals(2, execute("SELECT * FROM %s WHERE value[1] = 'v1'").size());
@@ -71,7 +71,7 @@ public class CollectionIndexingTest extends SAITester
     }
 
     @Test
-    public void indexFrozenList() throws Throwable
+    public void indexFrozenList()
     {
         createPopulatedFrozenList(createIndexDDL("FULL(value)"));
         assertEquals(2, execute("SELECT * FROM %s WHERE value = ?", Arrays.asList(1, 2, 3)).size());
@@ -176,6 +176,34 @@ public class CollectionIndexingTest extends SAITester
         assertUnsupportedIndexOperator(2, "SELECT * FROM %s WHERE value[1] = 'v1'");
     }
 
+    @Test
+    public void unindexedContainsExpressions()
+    {
+        createTable("CREATE TABLE %s (k int PRIMARY KEY, v int, m map<int, int>)");
+        createIndex("CREATE INDEX ON %s(v) USING 'SAI'"); // just to make sure that SAI is involved
+
+        Object[] row = row(0, 1, map(2, 3));
+        execute("INSERT INTO %s (k, v, m) VALUES (?, ?, ?)", row);
+        execute("INSERT INTO %s (k, v, m) VALUES (?, ?, ?)", 1, 1, map(12, 13));
+
+        // try without any indexes on the map
+        assertRows(execute("SELECT k, v, m FROM %s WHERE v = 1 AND m CONTAINS 3 ALLOW FILTERING"), row);
+        assertRows(execute("SELECT k, v, m FROM %s WHERE v = 1 AND m CONTAINS KEY 2 ALLOW FILTERING"), row);
+        assertRows(execute("SELECT k, v, m FROM %s WHERE v = 1 AND m CONTAINS KEY 2 AND m CONTAINS 3 ALLOW FILTERING"), row);
+
+        // try with index on map values
+        createIndex("CREATE INDEX ON %s(m) USING 'SAI'");
+        assertRows(execute("SELECT k, v, m FROM %s WHERE v = 1 AND m CONTAINS 3"), row);
+        assertRows(execute("SELECT k, v, m FROM %s WHERE v = 1 AND m CONTAINS KEY 2 ALLOW FILTERING"), row);
+        assertRows(execute("SELECT k, v, m FROM %s WHERE v = 1 AND m CONTAINS KEY 2 AND m CONTAINS 3 ALLOW FILTERING"), row);
+
+        // try with index on map keys
+        createIndex("CREATE INDEX ON %s(KEYS(m)) USING 'SAI'");
+        assertRows(execute("SELECT k, v, m FROM %s WHERE v = 1 AND m CONTAINS 3"), row);
+        assertRows(execute("SELECT k, v, m FROM %s WHERE v = 1 AND m CONTAINS KEY 2"), row);
+        assertRows(execute("SELECT k, v, m FROM %s WHERE v = 1 AND m CONTAINS KEY 2 AND m CONTAINS 3"), row);
+    }
+
     private void createPopulatedMap(String createIndex)
     {
         createTable("CREATE TABLE %s (pk int primary key, value map<int, text>)");
@@ -191,7 +219,7 @@ public class CollectionIndexingTest extends SAITester
     }
 
     @SuppressWarnings("SameParameterValue")
-    private void createPopulatedFrozenMap(String createIndex) throws Throwable
+    private void createPopulatedFrozenMap(String createIndex)
     {
         createTable("CREATE TABLE %s (pk int primary key, value frozen<map<int, text>>)");
         createIndex(createIndex);