diff --git a/plugin/src/main/java/org/opennms/timeseries/cortex/CortexTSS.java b/plugin/src/main/java/org/opennms/timeseries/cortex/CortexTSS.java
index 3bdde2d..ee7aa7d 100644
--- a/plugin/src/main/java/org/opennms/timeseries/cortex/CortexTSS.java
+++ b/plugin/src/main/java/org/opennms/timeseries/cortex/CortexTSS.java
@@ -233,15 +233,19 @@ public void store(final List<Sample> samples, String clientID) throws StorageExc
         final Request request = builder.build();
 
         LOG.trace("Writing: {}", writeRequest);
-        asyncHttpCallsBulkhead.executeCompletionStage(() -> executeAsync(request)).whenComplete((r, ex) -> {
-            if (ex == null) {
-                samplesWritten.mark(samplesSorted.size());
-            } else {
-                // FIXME: Data loss
-                samplesLost.mark(samples.size());
-                LOG.error("Error occurred while storing samples, sample will be lost.", ex);
-            }
-        });
+        // Block until the HTTP write completes. This ensures the ring buffer worker
+        // thread does not process the next batch until this write has landed, preserving
+        // per-series timestamp ordering across consecutive WriteRequests as required by
+        // the Prometheus Remote Write spec.
+        try {
+            asyncHttpCallsBulkhead.executeCompletionStage(() -> executeAsync(request)).toCompletableFuture().get(
+                    config.getWriteTimeoutInMs(), TimeUnit.MILLISECONDS);
+            samplesWritten.mark(samplesSorted.size());
+        } catch (Exception ex) {
+            samplesLost.mark(samplesSorted.size());
+            Throwable cause = ex.getCause() != null ? ex.getCause() : ex;
+            throw new StorageException("Failed to write samples to Prometheus: " + cause.getMessage(), cause);
+        }
     }
 
     private void persistExternalTags(final Sample s) {