diff --git a/lib/service.js b/lib/service.js
index 8e1036f23e..e1ef401bc6 100644
--- a/lib/service.js
+++ b/lib/service.js
@@ -70,6 +70,10 @@ AWS.Service = inherit({
 
     this.validateService();
     if (!this.config.endpoint) regionConfig.configureEndpoint(this);
+    if (this.api.signatureVersion === 'bearer') {
+      // bearer from API declaration may not be overridden by config.
+      this.config.signatureVersion = 'bearer';
+    }
 
     this.config.endpoint = this.endpointFromTemplate(this.config.endpoint);
     this.setEndpoint(this.config.endpoint);