diff --git a/src/index.js b/src/index.js
index 6685768..9d0595d 100644
--- a/src/index.js
+++ b/src/index.js
@@ -40,7 +40,7 @@ import { hideBin } from 'yargs/helpers'
     const patterns = []
 
     fileTypes.forEach((fileType) => {
-      patterns.push(`**/*.${fileType}`)
+      patterns.push(`**/*.${fileType}`, `**/*.${fileType.toUpperCase()}`)
     })
 
     if (ignore) {
diff --git a/src/utils.js b/src/utils.js
index b3ae791..3743f3f 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -22,7 +22,7 @@ const compression = async (filename, dry) => {
   const tempFilePath = path.join(os.tmpdir(), path.basename(filename))
 
   try {
-    const ext = path.extname(filename).slice(1)
+    const ext = path.extname(filename).slice(1).toLowerCase()
     if (!ext) {
       throw new Error(`Cannot determine file type for ${filename}; no extension found.`)
     }