diff --git a/snuba/query/processors/logical/hash_bucket_functions.py b/snuba/query/processors/logical/hash_bucket_functions.py
index 2359d7d434..2527b66fe5 100644
--- a/snuba/query/processors/logical/hash_bucket_functions.py
+++ b/snuba/query/processors/logical/hash_bucket_functions.py
@@ -1,10 +1,11 @@
 from typing import Sequence
 
-from snuba.query.expressions import Column, Expression, FunctionCall
+from snuba.query.expressions import Column, Expression, FunctionCall, Literal
 from snuba.query.logical import Query
 from snuba.query.processors.logical import LogicalQueryProcessor
 from snuba.query.query_settings import QuerySettings
 from snuba.utils.constants import ATTRIBUTE_BUCKETS
+from snuba.utils.hashes import fnv_1a
 
 
 class HashBucketFunctionTransformer(LogicalQueryProcessor):
@@ -17,6 +18,8 @@ class HashBucketFunctionTransformer(LogicalQueryProcessor):
 
     This transformer converts mapKeys(attr_str) to arrayConcat(mapKeys(attr_str_0), mapKeys(attr_str_1), ...)
     and the same for mapValues
+
+    It converts mapExists(attr_str, 'blah') to mapExists(attr_str_{hash('blah')%20}, 'blah')
     """
 
     def __init__(
@@ -26,7 +29,7 @@ def __init__(
         self.hash_bucket_names = hash_bucket_names
 
     def process_query(self, query: Query, query_settings: QuerySettings) -> None:
-        def transform_expression(exp: Expression) -> Expression:
+        def transform_map_keys_and_values_expression(exp: Expression) -> Expression:
             if not isinstance(exp, FunctionCall):
                 return exp
 
@@ -62,4 +65,36 @@ def transform_expression(exp: Expression) -> Expression:
                 ),
             )
 
-        query.transform_expressions(transform_expression)
+        def transform_map_contains_expression(exp: Expression) -> Expression:
+            if not isinstance(exp, FunctionCall):
+                return exp
+
+            if len(exp.parameters) != 2:
+                return exp
+
+            column = exp.parameters[0]
+            if not isinstance(column, Column):
+                return exp
+
+            if column.column_name not in self.hash_bucket_names:
+                return exp
+
+            if exp.function_name != "mapContains":
+                return exp
+
+            key = exp.parameters[1]
+            if not isinstance(key, Literal) or not isinstance(key.value, str):
+                return exp
+
+            bucket_idx = fnv_1a(key.value.encode("utf-8")) % ATTRIBUTE_BUCKETS
+            return FunctionCall(
+                alias=exp.alias,
+                function_name=exp.function_name,
+                parameters=(
+                    Column(None, None, f"{column.column_name}_{bucket_idx}"),
+                    key,
+                ),
+            )
+
+        query.transform_expressions(transform_map_keys_and_values_expression)
+        query.transform_expressions(transform_map_contains_expression)
diff --git a/snuba/web/rpc/common.py b/snuba/web/rpc/common.py
index 2afdf004fe..c61d6c409e 100644
--- a/snuba/web/rpc/common.py
+++ b/snuba/web/rpc/common.py
@@ -219,7 +219,6 @@ def trace_item_filters_to_expression(item_filter: TraceItemFilter) -> Expression
         if k.name in NORMALIZED_COLUMNS.keys():
             return f.isNotNull(column(k.name))
         if k.type == AttributeKey.Type.TYPE_STRING:
-            # TODO: this doesn't actually work yet, need to make mapContains work with hash mapper too
             return f.mapContains(column("attr_str"), literal(k.name))
         else:
             return f.mapContains(column("attr_num"), literal(k.name))
diff --git a/tests/query/processors/test_hash_bucket_functions_processor.py b/tests/query/processors/test_hash_bucket_functions_processor.py
index a12ad41652..a259ca1066 100644
--- a/tests/query/processors/test_hash_bucket_functions_processor.py
+++ b/tests/query/processors/test_hash_bucket_functions_processor.py
@@ -7,7 +7,7 @@
 from snuba.query import SelectedExpression
 from snuba.query.data_source.simple import Entity as QueryEntity
 from snuba.query.dsl import Functions as f
-from snuba.query.dsl import binary_condition, literal
+from snuba.query.dsl import binary_condition, column, literal
 from snuba.query.expressions import Column, FunctionCall
 from snuba.query.logical import Query
 from snuba.query.processors.logical.hash_bucket_functions import (
@@ -184,6 +184,36 @@
             ),
         ),
     ),
+    (
+        Query(
+            QueryEntity(EntityKey.EAP_SPANS, ColumnSet([])),
+            selected_columns=[
+                SelectedExpression(
+                    "unrelated",
+                    Column(None, None, "column2"),
+                ),
+            ],
+            condition=binary_condition(
+                "or",
+                f.mapContains(column("attr_str"), literal("blah"), alias="x"),
+                f.mapContains(column("attr_strz"), literal("blah"), alias="z"),
+            ),
+        ),
+        Query(
+            QueryEntity(EntityKey.EAP_SPANS, ColumnSet([])),
+            selected_columns=[
+                SelectedExpression(
+                    "unrelated",
+                    Column(None, None, "column2"),
+                ),
+            ],
+            condition=binary_condition(
+                "or",
+                f.mapContains(column("attr_str_2"), literal("blah"), alias="x"),
+                f.mapContains(column("attr_strz"), literal("blah"), alias="z"),
+            ),
+        ),
+    ),
 ]