diff --git a/.changes/next-release/bugfix-region-config-31f590e0.json b/.changes/next-release/bugfix-region-config-31f590e0.json
new file mode 100644
index 0000000000..18374a4fc3
--- /dev/null
+++ b/.changes/next-release/bugfix-region-config-31f590e0.json
@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "region_config",
+  "description": "Set signatureVersion to bearer explcitly when defined in service API"
+}
\ No newline at end of file
diff --git a/lib/region_config.js b/lib/region_config.js
index 2e8d0de628..b4c2401a28 100644
--- a/lib/region_config.js
+++ b/lib/region_config.js
@@ -64,11 +64,20 @@ function configureEndpoint(service) {
 
       // signature version
       if (!config.signatureVersion) {
-        config.signatureVersion = (service.api && service.api.signatureVersion) || 'v4';
+        // Note: config is a global object and should not be mutated here.
+        // However, we are retaining this line for backwards compatibility.
+        // The non-v4 signatureVersion will be set in a copied object below.
+        config.signatureVersion = 'v4';
       }
 
+      var useBearer = (service.api && service.api.signatureVersion) === 'bearer';
+
       // merge config
-      applyConfig(service, config);
+      applyConfig(service, Object.assign(
+        {},
+        config,
+        { signatureVersion: useBearer ? 'bearer' : config.signatureVersion }
+      ));
       return;
     }
   }