diff --git a/__tests__/__fixtures__/project-openapi/README.markdown b/__tests__/__fixtures__/project-openapi/README.markdown
new file mode 100644
index 0000000..3fd4432
--- /dev/null
+++ b/__tests__/__fixtures__/project-openapi/README.markdown
@@ -0,0 +1,3 @@
+This is a test README.
+
+It should not be picked up by `swagger-inline` and throw errors because it doesn't have any docblocks.
diff --git a/src/index.js b/src/index.js
index 181f1df..7024a81 100644
--- a/src/index.js
+++ b/src/index.js
@@ -134,7 +134,7 @@ function swaggerInline(globPatterns, providedOptions) {
                   });
                 } catch (err) {
                   // If the file that we failed to parse is a text file, let's just ignore it.
-                  if (['.json', '.md', '.txt'].includes(path.extname(fileInfo.fileName))) {
+                  if (['.json', '.md', '.markdown', '.txt'].includes(path.extname(fileInfo.fileName))) {
                     return Promise.resolve();
                   } else if (/Cannot find language definition/.test(err.message)) {
                     return Promise.resolve();