diff --git a/docker/configurator/index.js b/docker/configurator/index.js
index 1144d03b..df44f1da 100755
--- a/docker/configurator/index.js
+++ b/docker/configurator/index.js
@@ -16,9 +16,28 @@ const startMarkerIndex = originalHtmlContent.indexOf(START_MARKER)
 const endMarkerIndex = originalHtmlContent.indexOf(END_MARKER)
 
 const beforeStartMarkerContent = originalHtmlContent.slice(0, startMarkerIndex)
-const afterEndMarkerContent = originalHtmlContent.slice(endMarkerIndex + END_MARKER.length)
+const afterEndMarkerContent = originalHtmlContent.slice(
+  endMarkerIndex + END_MARKER.length
+)
 
-fs.writeFileSync(targetPath, `${beforeStartMarkerContent}
+if (startMarkerIndex < 0 || endMarkerIndex < 0) {
+  console.error("ERROR: Swagger UI was unable to inject Docker configuration data!")
+  console.error("!      This can happen when you provide custom HTML to Swagger UI.")
+  console.error("!  ")
+  console.error("!      In order to solve this, add the `Begin Swagger UI call region`")
+  console.error("!      and `End Swagger UI call region` markers to your HTML.")
+  console.error("!      See the repository for an example:")
+  console.error("!      https://github.com/swagger-api/swagger-ui/blob/02758b8125dbf38763cfd5d4f91c7c803e9bd0ad/dist/index.html#L40-L54")
+  console.error("!  ")
+  console.error("!      If you're seeing this message and aren't using custom HTML,")
+  console.error("!      this message may be a bug. Please file an issue:")
+  console.error("!      https://github.com/swagger-api/swagger-ui/issues/new/choose")
+  process.exit(0)
+}
+
+fs.writeFileSync(
+  targetPath,
+  `${beforeStartMarkerContent}
       ${START_MARKER}
       const ui = SwaggerUIBundle({
         ${indent(translator(process.env, { injectBaseConfig: true }), 8, 2)}
@@ -26,4 +45,5 @@ fs.writeFileSync(targetPath, `${beforeStartMarkerContent}
       
       ${indent(oauthBlockBuilder(process.env), 6, 2)}
       ${END_MARKER}
-${afterEndMarkerContent}`)
\ No newline at end of file
+${afterEndMarkerContent}`
+)