diff --git a/src/core/components/operation-tag.jsx b/src/core/components/operation-tag.jsx
index 1e71c587..b656714a 100644
--- a/src/core/components/operation-tag.jsx
+++ b/src/core/components/operation-tag.jsx
@@ -4,6 +4,7 @@ import ImPropTypes from "react-immutable-proptypes"
 import Im from "immutable"
 import { createDeepLinkPath, escapeDeepLinkPath, sanitizeUrl } from "core/utils"
 import { buildUrl } from "core/utils/url"
+import { isFunc } from "core/utils"
 
 export default class OperationTag extends React.Component {
 
@@ -55,8 +56,11 @@ export default class OperationTag extends React.Component {
 
     let tagDescription = tagObj.getIn(["tagDetails", "description"], null)
     let tagExternalDocsDescription = tagObj.getIn(["tagDetails", "externalDocs", "description"])
-    let rawTagExternalDocsUrl = tagObj.getIn(["tagDetails", "externalDocs", "url"])    
-    let tagExternalDocsUrl = buildUrl( rawTagExternalDocsUrl, specUrl, {selectedServer: oas3Selectors.selectedServer()} )
+    let rawTagExternalDocsUrl = tagObj.getIn(["tagDetails", "externalDocs", "url"])
+    let tagExternalDocsUrl
+    if (isFunc(oas3Selectors) && isFunc(oas3Selectors.selectedServer)) {
+      tagExternalDocsUrl = buildUrl( rawTagExternalDocsUrl, specUrl, { selectedServer: oas3Selectors.selectedServer() } )
+    }    
 
     let isShownKey = ["operations-tag", tag]
     let showTag = layoutSelectors.isShown(isShownKey, docExpansion === "full" || docExpansion === "list")