diff --git a/lib/config/definitions.js b/lib/config/definitions.js
index afc38f706971016b7eff924b0cd8c194c9c38356..7c805539710507a5fd62f850396d49ce0ac80808 100644
--- a/lib/config/definitions.js
+++ b/lib/config/definitions.js
@@ -154,7 +154,6 @@ const options = [
     description: 'String copy of npmrc file. Use \\n instead of line breaks',
     stage: 'branch',
     type: 'string',
-    mergeable: 'true',
   },
   {
     name: 'yarnrc',
diff --git a/lib/config/index.js b/lib/config/index.js
index 60ca1a110c1e9ceb1271291990dd3dccebf2a4de..97c850a381c6df6e88057f5b23d716bd1a049005 100644
--- a/lib/config/index.js
+++ b/lib/config/index.js
@@ -126,8 +126,6 @@ function mergeChildConfig(parentConfig, childConfig) {
         config[option.name] = (parentConfig[option.name] || []).concat(
           config[option.name] || []
         );
-      } else if (option.type === 'string') {
-        config[option.name] = parentConfig[option.name] + config[option.name];
       } else {
         config[option.name] = {
           ...parentConfig[option.name],
diff --git a/test/config/__snapshots__/index.spec.js.snap b/test/config/__snapshots__/index.spec.js.snap
index 56c31694d8c4b02c2a60b8953f2c7438bd966b87..73df5d60dca5903b72ce29704bc547a9a64c6cc9 100644
--- a/test/config/__snapshots__/index.spec.js.snap
+++ b/test/config/__snapshots__/index.spec.js.snap
@@ -1,12 +1,5 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`config/index mergeChildConfig(parentConfig, childConfig) handles mergeable strings 1`] = `
-"_auth=abcd-abcd-abcd-abcd
-always-auth=true
-registry=some-registry
-"
-`;
-
 exports[`config/index mergeChildConfig(parentConfig, childConfig) merges 1`] = `
 Object {
   "branchName": "{{branchPrefix}}lock-file-maintenance",
diff --git a/test/config/index.spec.js b/test/config/index.spec.js
index 87ddd5924f58f073b35b984553eb33f7ccc3dbbb..582a3cddd9fa06f0ae02a854ac704a5acfcf08b3 100644
--- a/test/config/index.spec.js
+++ b/test/config/index.spec.js
@@ -235,15 +235,5 @@ describe('config/index', () => {
       const config = configParser.mergeChildConfig(parentConfig, undefined);
       expect(config).toMatchObject(parentConfig);
     });
-    it('handles mergeable strings', () => {
-      const parentConfig = { ...defaultConfig };
-      parentConfig.npmrc = '_auth=abcd-abcd-abcd-abcd\n';
-      const childConfig = {
-        npmrc: 'always-auth=true\nregistry=some-registry\n',
-      };
-      const configParser = require('../../lib/config/index.js');
-      const config = configParser.mergeChildConfig(parentConfig, childConfig);
-      expect(config.npmrc).toMatchSnapshot();
-    });
   });
 });