diff --git a/docs/changelog/103690.yaml b/docs/changelog/103690.yaml
new file mode 100644
index 0000000000000..fa9076789c1cd
--- /dev/null
+++ b/docs/changelog/103690.yaml
@@ -0,0 +1,5 @@
+pr: 103690
+summary: Restore inter-segment search concurrency with synthetic source is enabled
+area: Search
+type: bug
+issues: []
diff --git a/server/src/main/java/org/elasticsearch/index/mapper/SourceLoader.java b/server/src/main/java/org/elasticsearch/index/mapper/SourceLoader.java
index 607ba2b261f5d..c07821f3c9ae7 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/SourceLoader.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/SourceLoader.java
@@ -20,6 +20,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
@@ -79,12 +80,15 @@ public Set<String> requiredStoredFields() {
      * Load {@code _source} from doc values.
      */
     class Synthetic implements SourceLoader {
-        private final SyntheticFieldLoader loader;
-        private final Map<String, SyntheticFieldLoader.StoredFieldLoader> storedFieldLoaders;
+        private final Supplier<SyntheticFieldLoader> syntheticFieldLoaderLeafSupplier;
+        private final Set<String> requiredStoredFields;
 
         public Synthetic(Mapping mapping) {
-            loader = mapping.syntheticFieldLoader();
-            storedFieldLoaders = Map.copyOf(loader.storedFieldLoaders().collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)));
+            this.syntheticFieldLoaderLeafSupplier = mapping::syntheticFieldLoader;
+            this.requiredStoredFields = syntheticFieldLoaderLeafSupplier.get()
+                .storedFieldLoaders()
+                .map(Map.Entry::getKey)
+                .collect(Collectors.toSet());
         }
 
         @Override
@@ -94,19 +98,26 @@ public boolean reordersFieldValues() {
 
         @Override
         public Set<String> requiredStoredFields() {
-            return storedFieldLoaders.keySet();
+            return requiredStoredFields;
         }
 
         @Override
         public Leaf leaf(LeafReader reader, int[] docIdsInLeaf) throws IOException {
-            return new SyntheticLeaf(loader.docValuesLoader(reader, docIdsInLeaf));
+            SyntheticFieldLoader loader = syntheticFieldLoaderLeafSupplier.get();
+            return new SyntheticLeaf(loader, loader.docValuesLoader(reader, docIdsInLeaf));
         }
 
-        private class SyntheticLeaf implements Leaf {
+        private static class SyntheticLeaf implements Leaf {
+            private final SyntheticFieldLoader loader;
             private final SyntheticFieldLoader.DocValuesLoader docValuesLoader;
+            private final Map<String, SyntheticFieldLoader.StoredFieldLoader> storedFieldLoaders;
 
-            private SyntheticLeaf(SyntheticFieldLoader.DocValuesLoader docValuesLoader) {
+            private SyntheticLeaf(SyntheticFieldLoader loader, SyntheticFieldLoader.DocValuesLoader docValuesLoader) {
+                this.loader = loader;
                 this.docValuesLoader = docValuesLoader;
+                this.storedFieldLoaders = Map.copyOf(
+                    loader.storedFieldLoaders().collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue))
+                );
             }
 
             @Override
diff --git a/server/src/main/java/org/elasticsearch/search/DefaultSearchContext.java b/server/src/main/java/org/elasticsearch/search/DefaultSearchContext.java
index a8721503c7454..773934615e051 100644
--- a/server/src/main/java/org/elasticsearch/search/DefaultSearchContext.java
+++ b/server/src/main/java/org/elasticsearch/search/DefaultSearchContext.java
@@ -32,7 +32,6 @@
 import org.elasticsearch.index.fielddata.FieldDataContext;
 import org.elasticsearch.index.fielddata.IndexFieldData;
 import org.elasticsearch.index.fielddata.IndexOrdinalsFieldData;
-import org.elasticsearch.index.mapper.DocumentMapper;
 import org.elasticsearch.index.mapper.IdLoader;
 import org.elasticsearch.index.mapper.MappedFieldType;
 import org.elasticsearch.index.mapper.NestedLookup;
@@ -167,20 +166,13 @@ final class DefaultSearchContext extends SearchContext {
             this.indexShard = readerContext.indexShard();
 
             Engine.Searcher engineSearcher = readerContext.acquireSearcher("search");
-            int maximumNumberOfSlices;
-            if (hasSyntheticSource(indexService)) {
-                // accessing synthetic source is not thread safe
-                maximumNumberOfSlices = 1;
-            } else {
-                maximumNumberOfSlices = determineMaximumNumberOfSlices(
-                    executor,
-                    request,
-                    resultsType,
-                    enableQueryPhaseParallelCollection,
-                    field -> getFieldCardinality(field, readerContext.indexService(), engineSearcher.getDirectoryReader())
-                );
-
-            }
+            int maximumNumberOfSlices = determineMaximumNumberOfSlices(
+                executor,
+                request,
+                resultsType,
+                enableQueryPhaseParallelCollection,
+                field -> getFieldCardinality(field, readerContext.indexService(), engineSearcher.getDirectoryReader())
+            );
             if (executor == null) {
                 this.searcher = new ContextIndexSearcher(
                     engineSearcher.getIndexReader(),
@@ -222,14 +214,6 @@ final class DefaultSearchContext extends SearchContext {
         }
     }
 
-    private static boolean hasSyntheticSource(IndexService indexService) {
-        DocumentMapper documentMapper = indexService.mapperService().documentMapper();
-        if (documentMapper != null) {
-            return documentMapper.sourceMapper().isSynthetic();
-        }
-        return false;
-    }
-
     static long getFieldCardinality(String field, IndexService indexService, DirectoryReader directoryReader) {
         MappedFieldType mappedFieldType = indexService.mapperService().fieldType(field);
         if (mappedFieldType == null) {
diff --git a/server/src/test/java/org/elasticsearch/search/DefaultSearchContextTests.java b/server/src/test/java/org/elasticsearch/search/DefaultSearchContextTests.java
index a531a74d956ee..9aa358123d282 100644
--- a/server/src/test/java/org/elasticsearch/search/DefaultSearchContextTests.java
+++ b/server/src/test/java/org/elasticsearch/search/DefaultSearchContextTests.java
@@ -395,8 +395,6 @@ public void testClearQueryCancellationsOnClose() throws IOException {
         when(indexShard.getThreadPool()).thenReturn(threadPool);
 
         IndexService indexService = mock(IndexService.class);
-        MapperService mapperService = mock(MapperService.class);
-        when(indexService.mapperService()).thenReturn(mapperService);
 
         try (Directory dir = newDirectory(); RandomIndexWriter w = new RandomIndexWriter(random(), dir)) {