diff --git a/packages/core/src/server/flecks.js b/packages/core/src/server/flecks.js
index 9c69264..94a6303 100644
--- a/packages/core/src/server/flecks.js
+++ b/packages/core/src/server/flecks.js
@@ -188,7 +188,7 @@ export default class ServerFlecks extends Flecks {
     if (needCompilation.length > 0) {
       const register = R('@babel/register');
       // Augment the compiler with babel config from flecksrc.
-      const rcBabelConfig = babelmerge(...this.babel(rcs).map(([, babel]) => babel));
+      const rcBabelConfig = babelmerge.all(this.babel(rcs).map(([, babel]) => babel));
       debug('.flecksrc: babel: %O', rcBabelConfig);
       // Key flecks needing compilation by their roots, so we can compile all common roots with a
       // single invocation of `@babel/register`.
@@ -566,7 +566,7 @@ export default class ServerFlecks extends Flecks {
           const babel = {
             configFile,
             // Augment the compiler with babel config from flecksrc.
-            ...babelmerge(...rcBabel.map(([, babel]) => babel)),
+            ...babelmerge.all(rcBabel.map(([, babel]) => babel)),
           };
           compileLoader({
             ignore: [sourceroot],
diff --git a/packages/fleck/src/server/build/fleck.neutrinorc.js b/packages/fleck/src/server/build/fleck.neutrinorc.js
index 79b81e0..034a06c 100644
--- a/packages/fleck/src/server/build/fleck.neutrinorc.js
+++ b/packages/fleck/src/server/build/fleck.neutrinorc.js
@@ -16,12 +16,12 @@ const config = require('../../../../core/src/bootstrap/fleck.neutrinorc');
 module.exports = async (flecks) => {
   // Compile.
   const rcBabel = flecks.babel();
-  debug('.flecksrc: babel: %O', rcBabel);
+  debug('.flecksrc: babel: %j', rcBabel);
   config.use.push(fleck({
-    babel: babelmerge(
+    babel: babelmerge.all([
       {configFile: flecks.buildConfig('babel.config.js')},
       ...rcBabel.map(([, babel]) => babel),
-    ),
+    ]),
   }));
   config.use.push(({config}) => {
     config.stats(flecks.get('@flecks/fleck/server.stats'));