diff --git a/handwritten/spanner/src/instrument.ts b/handwritten/spanner/src/instrument.ts
index 9537e51efd91..cd5132056f4f 100644
--- a/handwritten/spanner/src/instrument.ts
+++ b/handwritten/spanner/src/instrument.ts
@@ -25,7 +25,6 @@ import {
   context,
   trace,
   INVALID_SPAN_CONTEXT,
-  ROOT_CONTEXT,
   SpanAttributes,
   TimeInput,
   TracerProvider,
@@ -97,23 +96,27 @@ const {
   AsyncHooksContextManager,
 } = require('@opentelemetry/context-async-hooks');
 
+let contextManagerInstallAttempted = false;
+
 /*
- * This function ensures that async/await works correctly by
- * checking if context.active() returns an invalid/unset context
- * and if so, sets a global AsyncHooksContextManager otherwise
- * spans resulting from async/await invocations won't be correctly
- * associated in their respective hierarchies.
+ * If no global ContextManager is registered, install an AsyncHooksContextManager
+ * so that async/await trace context propagation works for apps that haven't
+ * configured OpenTelemetry themselves. If the host app has already installed a
+ * ContextManager, leave it alone — tearing down a working manager breaks the
+ * host's baggage and span parentage on the next gRPC call.
+ *
+ * setGlobalContextManager() returns false when a manager is already registered,
+ * which is the documented signal that we shouldn't replace it. The
+ * `contextManagerInstallAttempted` latch makes the call idempotent so we don't
+ * allocate a new AsyncHooksContextManager on each Spanner client construction.
  */
 function ensureInitialContextManagerSet() {
-  if (!context['_contextManager'] || context.active() === ROOT_CONTEXT) {
-    // If no context manager is currently set, or if the active context is the ROOT_CONTEXT,
-    // trace context propagation cannot
-    // function correctly with async/await for OpenTelemetry
-    // See {@link https://opentelemetry.io/docs/languages/js/context/#active-context}
-    context.disable(); // Disable any prior contextManager.
-    const contextManager = new AsyncHooksContextManager();
-    contextManager.enable();
-    context.setGlobalContextManager(contextManager);
+  if (contextManagerInstallAttempted) return;
+  contextManagerInstallAttempted = true;
+  const contextManager = new AsyncHooksContextManager();
+  contextManager.enable();
+  if (!context.setGlobalContextManager(contextManager)) {
+    contextManager.disable();
   }
 }