diff --git a/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-couchdb.yaml b/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-couchdb.yaml
index 1dfac4c9d..cbb673296 100644
--- a/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-couchdb.yaml
+++ b/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-couchdb.yaml
@@ -79,7 +79,7 @@ interactions:
                 - go-elasticsearch/7.17.10 (linux amd64; Go 1.22.1)
             X-Elastic-Client-Meta:
                 - es=7.17.10,go=1.22.1,t=7.17.10,hc=1.22.1
-        url: https://127.0.0.1:9200/_index_template/_simulate_index/metrics-couchdb.server-12345
+        url: https://127.0.0.1:9200/_index_template/_simulate_index/metrics-couchdb.server-12345simulated
         method: POST
       response:
         proto: HTTP/1.1
diff --git a/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-dummy.yaml b/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-dummy.yaml
index 4004b7c49..d79cbfe36 100644
--- a/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-dummy.yaml
+++ b/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-dummy.yaml
@@ -79,7 +79,7 @@ interactions:
                 - go-elasticsearch/7.17.10 (linux amd64; Go 1.22.1)
             X-Elastic-Client-Meta:
                 - es=7.17.10,go=1.22.1,t=7.17.10,hc=1.22.1
-        url: https://127.0.0.1:9200/_index_template/_simulate_index/logs-logs_synthetic_mode.synthetic-12345
+        url: https://127.0.0.1:9200/_index_template/_simulate_index/logs-logs_synthetic_mode.synthetic-12345simulated
         method: POST
       response:
         proto: HTTP/1.1
diff --git a/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-nginx-logsdb.yaml b/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-nginx-logsdb.yaml
index fee71806b..75cebda55 100644
--- a/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-nginx-logsdb.yaml
+++ b/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-nginx-logsdb.yaml
@@ -79,7 +79,7 @@ interactions:
                 - go-elasticsearch/7.17.10 (linux amd64; Go 1.22.1)
             X-Elastic-Client-Meta:
                 - es=7.17.10,go=1.22.1,t=7.17.10,hc=1.22.1
-        url: https://127.0.0.1:9200/_index_template/_simulate_index/logs-nginx.access-12345
+        url: https://127.0.0.1:9200/_index_template/_simulate_index/logs-nginx.access-12345simulated
         method: POST
       response:
         proto: HTTP/1.1
diff --git a/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-nginx.yaml b/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-nginx.yaml
index 9c2bf00ed..5c391025a 100644
--- a/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-nginx.yaml
+++ b/internal/testrunner/runners/system/testdata/elasticsearch-8-mock-synthetic-mode-nginx.yaml
@@ -79,7 +79,7 @@ interactions:
                 - go-elasticsearch/7.17.10 (linux amd64; Go 1.22.1)
             X-Elastic-Client-Meta:
                 - es=7.17.10,go=1.22.1,t=7.17.10,hc=1.22.1
-        url: https://127.0.0.1:9200/_index_template/_simulate_index/logs-nginx.access-12345
+        url: https://127.0.0.1:9200/_index_template/_simulate_index/logs-nginx.access-12345simulated
         method: POST
       response:
         proto: HTTP/1.1
diff --git a/internal/testrunner/runners/system/tester.go b/internal/testrunner/runners/system/tester.go
index cb2b73d23..e1026ebee 100644
--- a/internal/testrunner/runners/system/tester.go
+++ b/internal/testrunner/runners/system/tester.go
@@ -614,7 +614,9 @@ func (r *tester) runTestPerVariant(ctx context.Context, result *testrunner.Resul
 }
 
 func isSyntheticSourceModeEnabled(ctx context.Context, api *elasticsearch.API, dataStreamName string) (bool, error) {
-	resp, err := api.Indices.SimulateIndexTemplate(dataStreamName,
+	// We append a suffix so we don't use an existing resource, what may cause conflicts in old versions of
+	// Elasticsearch, such as https://github.com/elastic/elasticsearch/issues/84256.
+	resp, err := api.Indices.SimulateIndexTemplate(dataStreamName+"simulated",
 		api.Indices.SimulateIndexTemplate.WithContext(ctx),
 	)
 	if err != nil {