diff --git a/docs/changelog/89114.yaml b/docs/changelog/89114.yaml
new file mode 100644
index 0000000000000..c363437586249
--- /dev/null
+++ b/docs/changelog/89114.yaml
@@ -0,0 +1,5 @@
+pr: 89114
+summary: Don't modify source map when parsing composite runtime field
+area: Mapping
+type: bug
+issues: []
diff --git a/modules/runtime-fields-common/src/yamlRestTest/resources/rest-api-spec/test/runtime_fields/111_search_time_composite.yml b/modules/runtime-fields-common/src/yamlRestTest/resources/rest-api-spec/test/runtime_fields/111_search_time_composite.yml
new file mode 100644
index 0000000000000..dc10d16c26ca3
--- /dev/null
+++ b/modules/runtime-fields-common/src/yamlRestTest/resources/rest-api-spec/test/runtime_fields/111_search_time_composite.yml
@@ -0,0 +1,36 @@
+---
+setup:
+  - do:
+      indices.create:
+        index: test
+        body:
+          settings:
+            number_of_shards: 2
+            number_of_replicas: 0
+  - do:
+      bulk:
+        index: test
+        refresh: true
+        body: |
+          {"index":{}}
+          {"A":2}
+
+---
+"search-time composite across multiple shards":
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            term:
+              "r.shouldReturn" : true
+          runtime_mappings:
+            r:
+              type: composite
+              fields:
+                shouldReturn:
+                  type: boolean
+              script:
+                source: "emit('shouldReturn',true)"
+
+  - match: {hits.total.value: 1}
diff --git a/server/src/main/java/org/elasticsearch/index/mapper/CompositeRuntimeField.java b/server/src/main/java/org/elasticsearch/index/mapper/CompositeRuntimeField.java
index a8e9b487160de..ea8fbb0dcd60b 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/CompositeRuntimeField.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/CompositeRuntimeField.java
@@ -17,6 +17,7 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
@@ -85,7 +86,12 @@ protected RuntimeField createRuntimeField(MappingParserContext parserContext) {
                 name,
                 lookup -> factory.newFactory(name, script.get().getParams(), lookup)
             );
-            Map<String, RuntimeField> runtimeFields = RuntimeField.parseRuntimeFields(fields.getValue(), parserContext, builder, false);
+            Map<String, RuntimeField> runtimeFields = RuntimeField.parseRuntimeFields(
+                new HashMap<>(fields.getValue()),
+                parserContext,
+                builder,
+                false
+            );
             return new CompositeRuntimeField(name, getParameters(), runtimeFields.values());
         }
     });
@@ -118,11 +124,6 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
         for (FieldMapper.Parameter<?> parameter : parameters) {
             parameter.toXContent(builder, includeDefaults);
         }
-        builder.startObject("fields");
-        for (RuntimeField subfield : subfields) {
-            subfield.toXContent(builder, params);
-        }
-        builder.endObject();
         builder.endObject();
         return builder;
     }