diff --git a/packages/mosaic/src/stages/gateway-config.ts b/packages/mosaic/src/stages/gateway-config.ts
index fdfd8ba..6002169 100644
--- a/packages/mosaic/src/stages/gateway-config.ts
+++ b/packages/mosaic/src/stages/gateway-config.ts
@@ -294,7 +294,12 @@ export async function gatewayConfigStage(
   }
 
   // Install the gateway npm package on first install or after failure.
-  if (!opts.skipInstall && !daemonRunning) {
+  // MOSAIC_GATEWAY_SKIP_NPM_INSTALL=1 forces a skip even without opts.skipInstall:
+  // used by dev/offline installs where @mosaicstack/gateway is already present
+  // globally (e.g. a build-from-source `install.sh --dev`) and must not be
+  // overwritten by the registry @latest build.
+  const skipNpmInstall = opts.skipInstall || process.env['MOSAIC_GATEWAY_SKIP_NPM_INSTALL'] === '1';
+  if (!skipNpmInstall && !daemonRunning) {
     installGatewayPackage();
   }