diff --git a/lib/manager/npm/registry.js b/lib/manager/npm/registry.js
index 1a5aeca088753ff740c34856fe5f89ec011d4b41..cc600e2b8105565b9ed81c3dfd91c5c361747976 100644
--- a/lib/manager/npm/registry.js
+++ b/lib/manager/npm/registry.js
@@ -48,6 +48,11 @@ function setNpmrc(input, exposeEnv = false) {
 }
 
 function envReplace(value, env = process.env) {
+  // istanbul ignore if
+  if (typeof value !== 'string' || !value) {
+    return value;
+  }
+
   const ENV_EXPR = /(\\*)\$\{([^}]+)\}/g;
 
   return value.replace(ENV_EXPR, (match, esc, envVarName) => {